Is there any kind of hash code function in JavaScript

Question

Basically  I m trying to create an object of unique objects  a set  I had the brilliant idea of just using a JavaScript object with objects for the property names  Such as   set obj    true    This works  up to a point  It works great with string and numbers  but with other objects  they all seem to  hash  to the same value and access the same property  Is there some kind of way I can generate a unique hash value for an object  How do strings and numbers do it  can I override the same behavior

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I will try to go a little deeper than other answers.

Even if JS had better hashing support it would not magically hash everything perfectly, in many cases you will have to define your own hash function. For example Java has good hashing support, but you still have to think and do some work.

One problem is with the term hash/hashcode ... there is cryptographic hashing and non-cryptographic hashing. The other problem, is you have to understand why hashing is useful and how it works.

When we talk about hashing in JavaScript or Java most of the time we are talking about non-cryptographic hashing, usually about hashing for hashmap/hashtable (unless we are working on authentication or passwords, which you could be doing server-side using NodeJS ...).

It depends on what data you have and what you want to achieve.

Your data has some natural "simple" uniqueness:

The hash of an integer is ... the integer, as it is unique, lucky you !
The hash of a string ... it depends on the string, if the string represents a unique identifier, you may consider it as a hash (so no hashing needed).
Anything which is indirectly pretty much a unique integer is the simplest case
This will respect: hashcode equal if objects are equal

Your data has some natural "composite" uniqueness:

For example with a person object, you may compute a hash using firstname, lastname, birthdate, ... see how Java does it: Good Hash Function for Strings, or use some other ID info that is cheap and unique enough for your usecase

You have no idea what your data will be:

Good luck ... you could serialize to string and hash it Java style, but that may be expensive if the string is large and it will not avoid collisions as well as say the hash of an integer (self).

There is no magically efficient hashing technique for unknown data, in some cases it is quite easy, in other cases you may have to think twice. So even if JavaScript/ECMAScript adds more support, there is no magic language solution for this problem.

In practice you need two things: enough uniqueness, enough speed

In addition to that it is great to have: "hashcode equal if objects are equal"

User · Answer

If you truly want set behavior  I m going by Java knowledge   then you will be hard pressed to find a solution in JavaScript  Most developers will recommend a unique key to represent each object  but this is unlike set  in that you can get two identical objects each with a unique key  The Java API does the work of checking for duplicate values by comparing hash code values  not keys  and since there is no hash code value representation of objects in JavaScript  it becomes almost impossible to do the same  Even the Prototype JS library admits this shortcoming  when it says       Hash can be thought of as an   associative array  binding unique keys   to values  which are not necessarily   unique        http   www prototypejs org api hash

User · Answer

If you truly want set behavior  I m going by Java knowledge   then you will be hard pressed to find a solution in JavaScript  Most developers will recommend a unique key to represent each object  but this is unlike set  in that you can get two identical objects each with a unique key  The Java API does the work of checking for duplicate values by comparing hash code values  not keys  and since there is no hash code value representation of objects in JavaScript  it becomes almost impossible to do the same  Even the Prototype JS library admits this shortcoming  when it says       Hash can be thought of as an   associative array  binding unique keys   to values  which are not necessarily   unique        http   www prototypejs org api hash

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The easiest way to do this is to give each of your objects its own unique toString method    function         var id   0         global MyObject        MyObject   function             this objectId     lt  MyObject      id        gt            this toString  function                 return this objectId                            I had the same problem and this solved it perfectly for me with minimal fuss  and was a lot easier that re-implementing some fatty Java style Hashtable and adding equals   and hashCode   to your object classes  Just make sure that you don t also stick a string   lt  MyObject 12  into your hash or it will wipe out the entry for your exiting object with that id   Now all my hashes are totally chill  I also just posted a blog entry a few days ago about this exact topic

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The JavaScript specification defines indexed property access as performing a toString conversion on the index name  For example   myObject myProperty           is the same as  myObject myProperty toString             This is necessary as in JavaScript  myObject  someProperty     is the same as  myObject someProperty   And yes  it makes me sad as well  -

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In ECMAScript 6 there s now a Set that works how you d like  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Set  It s already available in the latest Chrome  FF  and IE11

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Just use hidden secret property with the defineProperty enumerable  false  It work very fast    The first read uniqueId  1 257 500 ops s All others  309 226 485 ops s   var nextObjectId   1 function getNextObjectId         return nextObjectId      var UNIQUE ID PROPERTY NAME    458d576952bc489ab45e98ac7f296fd9  function getObjectUniqueId object        if  object    null            return null            var id   object UNIQUE ID PROPERTY NAME       if  id    null            return id            if  Object isFrozen object             return null            var uniqueId   getNextObjectId       Object defineProperty object  UNIQUE ID PROPERTY NAME            enumerable  false          configurable  false          writable  false          value  uniqueId              return uniqueId

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The JavaScript specification defines indexed property access as performing a toString conversion on the index name  For example   myObject myProperty           is the same as  myObject myProperty toString             This is necessary as in JavaScript  myObject  someProperty     is the same as  myObject someProperty   And yes  it makes me sad as well  -

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Based on the title  we can generate strong SHA hashes  in a browser context  it can be used to generate a unique hash from an object  an array of params  a string  or whatever   x000D   x000D  async function H m      const msgUint8   new TextEncoder   encode m                           const hashBuffer   await crypto subtle digest  SHA-256   msgUint8              const hashArray   Array from new Uint8Array hashBuffer                         const hashHex   hashArray map b   gt  b toString 16  padStart 2   0    join       console log hashHex        Examples -----------------------    H  An obscure        H JSON stringify    hello     world      H JSON stringify   54 51 54 47     x000D   x000D   x000D   The above output in my browser  it should be equal for you too  bf1cf3fe6975fe382ab392ec1dd42009380614be03d489f23601c11413cfca2b 93a23971a914e5eacbf0a8d25154cda309c3c1c72fbb9914d47c60f3cb681588 d2f209e194045604a3b15bdfd7502898a0e848e4603c5a818bd01da69c00ad19  Supported algos  SHA-1  but don t use this in cryptographic applications  SHA-256 SHA-384 SHA-512  https   developer mozilla org en-US docs Web API SubtleCrypto digest Converting a digest to a hex string

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The solution I chose is similar to Daniel s  but rather than use an object factory and override the toString  I explicitly add the hash to the object when it is first requested through a getHashCode function  A little messy  but better for my needs     Function prototype getHashCode    function id        return function             if   this hashCode                this hashCode     lt hash       id        gt                      return this hashCode          0

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If you want a hashCode   function like Java s in JavaScript  that is yours   String prototype hashCode   function        var hash   0      for  var i   0  i  lt  this length  i              var character   this charCodeAt i           hash     hash lt  lt 5 -hash  character          hash   hash  amp  hash     Convert to 32bit integer           return hash      That is the way of implementation in Java  bitwise operator    Please note that hashCode could be positive and negative  and that s normal  see HashCode giving negative values  So  you could consider to use Math abs   along with this function

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If you want to have unique values in a lookup object you can do something like this   Creating a lookup object  var lookup         Setting up the hashcode function  function getHashCode obj        var hashCode           if  typeof obj      object           return hashCode   obj      for  var prop in obj     No hasOwnProperty needed         hashCode    prop   getHashCode obj prop       Add key   value to the result string     return hashCode      Object  var key   getHashCode   1  3  3  7        key    1337  lookup key    true    Array  var key   getHashCode  1  3  3  7       key    01132337  lookup key    true    Other types  var key   getHashCode  StackOverflow       key    StackOverflow  lookup key    true    Final result    1337  true  01132337  true  StackOverflow  true    Do note that getHashCode doesn t return any value when the object or array is empty  getHashCode                  012  getHashCode                  012    This is similar to  ijmacd solution only getHashCode doesn t has the JSON dependency

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If you want to have unique values in a lookup object you can do something like this   Creating a lookup object  var lookup         Setting up the hashcode function  function getHashCode obj        var hashCode           if  typeof obj      object           return hashCode   obj      for  var prop in obj     No hasOwnProperty needed         hashCode    prop   getHashCode obj prop       Add key   value to the result string     return hashCode      Object  var key   getHashCode   1  3  3  7        key    1337  lookup key    true    Array  var key   getHashCode  1  3  3  7       key    01132337  lookup key    true    Other types  var key   getHashCode  StackOverflow       key    StackOverflow  lookup key    true    Final result    1337  true  01132337  true  StackOverflow  true    Do note that getHashCode doesn t return any value when the object or array is empty  getHashCode                  012  getHashCode                  012    This is similar to  ijmacd solution only getHashCode doesn t has the JSON dependency

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Just use hidden secret property with the defineProperty enumerable  false  It work very fast    The first read uniqueId  1 257 500 ops s All others  309 226 485 ops s   var nextObjectId   1 function getNextObjectId         return nextObjectId      var UNIQUE ID PROPERTY NAME    458d576952bc489ab45e98ac7f296fd9  function getObjectUniqueId object        if  object    null            return null            var id   object UNIQUE ID PROPERTY NAME       if  id    null            return id            if  Object isFrozen object             return null            var uniqueId   getNextObjectId       Object defineProperty object  UNIQUE ID PROPERTY NAME            enumerable  false          configurable  false          writable  false          value  uniqueId              return uniqueId

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Reference  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Symbol  you can use Es6 symbol to create unique key and access object      Every symbol value returned from Symbol   is unique   A symbol value may be used as an identifier for object properties  this is the data type s only purpose    var obj        obj Symbol  a       a   obj Symbol for  b       b   obj  c      c   obj d    d

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The JavaScript specification defines indexed property access as performing a toString conversion on the index name  For example   myObject myProperty           is the same as  myObject myProperty toString             This is necessary as in JavaScript  myObject  someProperty     is the same as  myObject someProperty   And yes  it makes me sad as well  -

User · Answer

For my specific situation I only care about the equality of the object as far as keys and primitive values go  The solution that worked for me was converting the object to its JSON representation and using that as the hash  There are limitations such as order of key definition potentially being inconsistent  but like I said it worked for me because these objects were all being generated in one place   var hashtable        var myObject    a 0 b 1 c 2    var hash   JSON stringify myObject         a  0  b  1  c  2    hashtable hash    myObject               a  0  b  1  c  2    myObject

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JavaScript objects can only use strings as keys  anything else is converted to a string    You could  alternatively  maintain an array which indexes the objects in question  and use its index string as a reference to the object  Something like this   var ObjectReference       ObjectReference push obj    set  ObjectReference     ObjectReference indexOf obj     true    Obviously it s a little verbose  but you could write a couple of methods that handle it and get and set all willy nilly   Edit      Your guess is fact -- this is defined behaviour in JavaScript -- specifically a toString conversion occurs meaning that you can can define your own toString function on the object that will be used as the property name  - olliej   This brings up another interesting point  you can define a toString method on the objects you want to hash  and that can form their hash identifier

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I put together a small JavaScript module a while ago to produce hashcodes for strings  objects  arrays  etc   I just committed it to GitHub       Usage   Hashcode value  stackoverflow      -2559914341 Hashcode value    site     stackoverflow        -3579752159

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The solution I chose is similar to Daniel s  but rather than use an object factory and override the toString  I explicitly add the hash to the object when it is first requested through a getHashCode function  A little messy  but better for my needs     Function prototype getHashCode    function id        return function             if   this hashCode                this hashCode     lt hash       id        gt                      return this hashCode          0

User · Answer

In ECMAScript 6 there s now a Set that works how you d like  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Set  It s already available in the latest Chrome  FF  and IE11

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What you described is covered by Harmony WeakMaps  part of the ECMAScript nbsp 6 specification  next version of JavaScript   That is  a set where the keys can be anything  including undefined  and is non-enumerable   This means it s impossible to get a reference to a value unless you have a direct reference to the key  any object   that links to it  It s important for a bunch of engine implementation reasons relating to efficiency and garbage collection  but it s also super cool for in that it allows for new semantics like revokable access permissions and passing data without exposing the data sender   From MDN   var wm1   new WeakMap        wm2   new WeakMap    var o1           o2   function          o3   window   wm1 set o1  37   wm1 set o2   azerty    wm2 set o1  o2      A value can be anything  including an object or a function  wm2 set o3  undefined   wm2 set wm1  wm2      Keys and values can be any objects  Even WeakMaps   wm1 get o2       azerty  wm2 get o2      Undefined  because there is no value for o2 on wm2  wm2 get o3      Undefined  because that is the set value   wm1 has o2      True wm2 has o2      False wm2 has o3      True  even if the value itself is  undefined     wm1 has o1        True wm1 delete o1   wm1 has o1        False   WeakMaps are available in current Firefox  Chrome and Edge  They re also supported in Node v7   and in v6 with the --harmony-weak-maps flag

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Here s my simple solution that returns a unique integer   function hashcode obj        var hc   0      var chars   JSON stringify obj  replace                g           var len   chars length      for  var i   0  i  lt  len  i                 Bump 7 to larger prime number to increase uniqueness         hc     chars charCodeAt i    7             return hc

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What you described is covered by Harmony WeakMaps  part of the ECMAScript nbsp 6 specification  next version of JavaScript   That is  a set where the keys can be anything  including undefined  and is non-enumerable   This means it s impossible to get a reference to a value unless you have a direct reference to the key  any object   that links to it  It s important for a bunch of engine implementation reasons relating to efficiency and garbage collection  but it s also super cool for in that it allows for new semantics like revokable access permissions and passing data without exposing the data sender   From MDN   var wm1   new WeakMap        wm2   new WeakMap    var o1           o2   function          o3   window   wm1 set o1  37   wm1 set o2   azerty    wm2 set o1  o2      A value can be anything  including an object or a function  wm2 set o3  undefined   wm2 set wm1  wm2      Keys and values can be any objects  Even WeakMaps   wm1 get o2       azerty  wm2 get o2      Undefined  because there is no value for o2 on wm2  wm2 get o3      Undefined  because that is the set value   wm1 has o2      True wm2 has o2      False wm2 has o3      True  even if the value itself is  undefined     wm1 has o1        True wm1 delete o1   wm1 has o1        False   WeakMaps are available in current Firefox  Chrome and Edge  They re also supported in Node v7   and in v6 with the --harmony-weak-maps flag

User · Answer

I put together a small JavaScript module a while ago to produce hashcodes for strings  objects  arrays  etc   I just committed it to GitHub       Usage   Hashcode value  stackoverflow      -2559914341 Hashcode value    site     stackoverflow        -3579752159

User · Answer

Based on the title  we can generate strong SHA hashes  in a browser context  it can be used to generate a unique hash from an object  an array of params  a string  or whatever   x000D   x000D  async function H m      const msgUint8   new TextEncoder   encode m                           const hashBuffer   await crypto subtle digest  SHA-256   msgUint8              const hashArray   Array from new Uint8Array hashBuffer                         const hashHex   hashArray map b   gt  b toString 16  padStart 2   0    join       console log hashHex        Examples -----------------------    H  An obscure        H JSON stringify    hello     world      H JSON stringify   54 51 54 47     x000D   x000D   x000D   The above output in my browser  it should be equal for you too  bf1cf3fe6975fe382ab392ec1dd42009380614be03d489f23601c11413cfca2b 93a23971a914e5eacbf0a8d25154cda309c3c1c72fbb9914d47c60f3cb681588 d2f209e194045604a3b15bdfd7502898a0e848e4603c5a818bd01da69c00ad19  Supported algos  SHA-1  but don t use this in cryptographic applications  SHA-256 SHA-384 SHA-512  https   developer mozilla org en-US docs Web API SubtleCrypto digest Converting a digest to a hex string

User · Answer

For my specific situation I only care about the equality of the object as far as keys and primitive values go  The solution that worked for me was converting the object to its JSON representation and using that as the hash  There are limitations such as order of key definition potentially being inconsistent  but like I said it worked for me because these objects were all being generated in one place   var hashtable        var myObject    a 0 b 1 c 2    var hash   JSON stringify myObject         a  0  b  1  c  2    hashtable hash    myObject               a  0  b  1  c  2    myObject

User · Answer

Reference  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Symbol  you can use Es6 symbol to create unique key and access object      Every symbol value returned from Symbol   is unique   A symbol value may be used as an identifier for object properties  this is the data type s only purpose    var obj        obj Symbol  a       a   obj Symbol for  b       b   obj  c      c   obj d    d

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If you want a hashCode   function like Java s in JavaScript  that is yours   String prototype hashCode   function        var hash   0      for  var i   0  i  lt  this length  i              var character   this charCodeAt i           hash     hash lt  lt 5 -hash  character          hash   hash  amp  hash     Convert to 32bit integer           return hash      That is the way of implementation in Java  bitwise operator    Please note that hashCode could be positive and negative  and that s normal  see HashCode giving negative values  So  you could consider to use Math abs   along with this function

User · Answer

My solution introduces a static function for the global Object object    function         var lastStorageId   0       this Object hash   function object            var hash   object   id           if   hash               hash   object   id   lastStorageId             return       hash                 I think this is more convenient with other object manipulating functions in JavaScript

User · Answer

The JavaScript specification defines indexed property access as performing a toString conversion on the index name  For example   myObject myProperty           is the same as  myObject myProperty toString             This is necessary as in JavaScript  myObject  someProperty     is the same as  myObject someProperty   And yes  it makes me sad as well  -

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I combined the answers from eyelidlessness and KimKha   The following is an angularjs service and it supports numbers  strings  and objects   exports Hash        gt      let hashFunc    function stringHash string  noType        let hashString   string      if   noType          hashString    string  string              var hash   0      for  var i   0  i  lt  hashString length  i              var character   hashString charCodeAt i           hash     hash lt  lt 5 -hash  character          hash   hash  amp  hash     Convert to 32bit integer           return hash         function objectHash obj  exclude        if  exclude indexOf obj   gt  -1          return undefined            let hash           const keys   Object keys obj  sort        for  let index   0  index  lt  keys length  index    1          const key   keys index         const keyHash   hashFunc key         const attrHash   hashFunc obj key   exclude         exclude push obj key          hash    stringHash  object  keyHash   attrHash    true             return stringHash hash  true          function Hash unkType  exclude        let ex   exclude      if  ex     undefined          ex                 if   isNaN unkType   amp  amp  typeof unkType      string           return unkType            switch  typeof unkType          case  object           return objectHash unkType  ex         default          return stringHash String unkType                 hashFunc   Hash     return Hash       Example Usage   Hash  hello world    Hash  hello world      Hash  hello world   Hash  hello   hello world     Hash  hello   hello world       Hash  hello   hello world    Hash  hello   hello world   goodbye   adios amigos     Hash  hello   hello world   goodbye   adios amigos       Hash  goodbye   adios amigos   hello   hello world    Hash   hello world     Hash   hello world       Hash   hello world    Hash 1   Hash 1     Hash 1  Hash  1    Hash  1      Hash  1     Output  432700947 true -411117486 true 1725787021 true -1585332251 true 1 true -1881759168 true   Explanation  As you can see the heart of the service is the hash function created by KimKha I have added types to the strings so that the sturucture of the object would also impact the final hash value The keys are hashed to prevent array object collisions   eyelidlessness object comparision is used to prevent infinit recursion by self referencing objects   Usage  I created this service so that I could have an error service that is accessed with objects  So that one service can register an error with a given object and another can determine if any errors were found   ie  JsonValidation js  ErrorSvc  id  1  json    attr   not-valid       Invalid Json Syntax - key not double quoted      UserOfData js  ErrorSvc  id  1  json    attr   not-valid         This would return     Invalid Json Syntax - key not double quoted     While  ErrorSvc  id  1  json     attr    not-valid         This would return

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JavaScript objects can only use strings as keys  anything else is converted to a string    You could  alternatively  maintain an array which indexes the objects in question  and use its index string as a reference to the object  Something like this   var ObjectReference       ObjectReference push obj    set  ObjectReference     ObjectReference indexOf obj     true    Obviously it s a little verbose  but you could write a couple of methods that handle it and get and set all willy nilly   Edit      Your guess is fact -- this is defined behaviour in JavaScript -- specifically a toString conversion occurs meaning that you can can define your own toString function on the object that will be used as the property name  - olliej   This brings up another interesting point  you can define a toString method on the objects you want to hash  and that can form their hash identifier

User · Answer

I will try to go a little deeper than other answers.

Even if JS had better hashing support it would not magically hash everything perfectly, in many cases you will have to define your own hash function. For example Java has good hashing support, but you still have to think and do some work.

One problem is with the term hash/hashcode ... there is cryptographic hashing and non-cryptographic hashing. The other problem, is you have to understand why hashing is useful and how it works.

When we talk about hashing in JavaScript or Java most of the time we are talking about non-cryptographic hashing, usually about hashing for hashmap/hashtable (unless we are working on authentication or passwords, which you could be doing server-side using NodeJS ...).

It depends on what data you have and what you want to achieve.

Your data has some natural "simple" uniqueness:

The hash of an integer is ... the integer, as it is unique, lucky you !
The hash of a string ... it depends on the string, if the string represents a unique identifier, you may consider it as a hash (so no hashing needed).
Anything which is indirectly pretty much a unique integer is the simplest case
This will respect: hashcode equal if objects are equal

Your data has some natural "composite" uniqueness:

For example with a person object, you may compute a hash using firstname, lastname, birthdate, ... see how Java does it: Good Hash Function for Strings, or use some other ID info that is cheap and unique enough for your usecase

You have no idea what your data will be:

Good luck ... you could serialize to string and hash it Java style, but that may be expensive if the string is large and it will not avoid collisions as well as say the hash of an integer (self).

There is no magically efficient hashing technique for unknown data, in some cases it is quite easy, in other cases you may have to think twice. So even if JavaScript/ECMAScript adds more support, there is no magic language solution for this problem.

In practice you need two things: enough uniqueness, enough speed

In addition to that it is great to have: "hashcode equal if objects are equal"

User · Answer

Here s my simple solution that returns a unique integer   function hashcode obj        var hc   0      var chars   JSON stringify obj  replace                g           var len   chars length      for  var i   0  i  lt  len  i                 Bump 7 to larger prime number to increase uniqueness         hc     chars charCodeAt i    7             return hc

User · Answer

If you truly want set behavior  I m going by Java knowledge   then you will be hard pressed to find a solution in JavaScript  Most developers will recommend a unique key to represent each object  but this is unlike set  in that you can get two identical objects each with a unique key  The Java API does the work of checking for duplicate values by comparing hash code values  not keys  and since there is no hash code value representation of objects in JavaScript  it becomes almost impossible to do the same  Even the Prototype JS library admits this shortcoming  when it says       Hash can be thought of as an   associative array  binding unique keys   to values  which are not necessarily   unique        http   www prototypejs org api hash

User · Answer

In addition to eyelidlessness s answer  here is a function that returns a reproducible  unique ID for any object   var uniqueIdList       function getConstantUniqueIdFor element           HACK  using a list results in O n   but how do we hash e g  a DOM node      if  uniqueIdList indexOf element   lt  0            uniqueIdList push element             return uniqueIdList indexOf element       As you can see it uses a list for look-up which is very inefficient  however that s the best I could find for now

User · Answer

JavaScript objects can only use strings as keys  anything else is converted to a string    You could  alternatively  maintain an array which indexes the objects in question  and use its index string as a reference to the object  Something like this   var ObjectReference       ObjectReference push obj    set  ObjectReference     ObjectReference indexOf obj     true    Obviously it s a little verbose  but you could write a couple of methods that handle it and get and set all willy nilly   Edit      Your guess is fact -- this is defined behaviour in JavaScript -- specifically a toString conversion occurs meaning that you can can define your own toString function on the object that will be used as the property name  - olliej   This brings up another interesting point  you can define a toString method on the objects you want to hash  and that can form their hash identifier

User · Answer

My solution introduces a static function for the global Object object    function         var lastStorageId   0       this Object hash   function object            var hash   object   id           if   hash               hash   object   id   lastStorageId             return       hash                 I think this is more convenient with other object manipulating functions in JavaScript

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If you want to use objects as keys you need to overwrite their toString Method  as some already mentioned here  The hash functions that were used are all fine  but they only work for the same objects not for equal objects   I ve written a small library that creates hashes from objects  which you can easily use for this purpose  The objects can even have a different order  the hashes will be the same  Internally you can use different types for your hash  djb2  md5  sha1  sha256  sha512  ripemd160    Here is a small example from the documentation   var hash   require  es-hash        Save data in an object with an object as a key Object prototype toString   function          return   object Object    hash this          var foo        foo  bar   foo       foo          Output      foo     undefined     console log foo  bar   foo      console log foo         The package can be used either in browser and in Node-Js   Repository  https   bitbucket org tehrengruber es-js-hash

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I combined the answers from eyelidlessness and KimKha   The following is an angularjs service and it supports numbers  strings  and objects   exports Hash        gt      let hashFunc    function stringHash string  noType        let hashString   string      if   noType          hashString    string  string              var hash   0      for  var i   0  i  lt  hashString length  i              var character   hashString charCodeAt i           hash     hash lt  lt 5 -hash  character          hash   hash  amp  hash     Convert to 32bit integer           return hash         function objectHash obj  exclude        if  exclude indexOf obj   gt  -1          return undefined            let hash           const keys   Object keys obj  sort        for  let index   0  index  lt  keys length  index    1          const key   keys index         const keyHash   hashFunc key         const attrHash   hashFunc obj key   exclude         exclude push obj key          hash    stringHash  object  keyHash   attrHash    true             return stringHash hash  true          function Hash unkType  exclude        let ex   exclude      if  ex     undefined          ex                 if   isNaN unkType   amp  amp  typeof unkType      string           return unkType            switch  typeof unkType          case  object           return objectHash unkType  ex         default          return stringHash String unkType                 hashFunc   Hash     return Hash       Example Usage   Hash  hello world    Hash  hello world      Hash  hello world   Hash  hello   hello world     Hash  hello   hello world       Hash  hello   hello world    Hash  hello   hello world   goodbye   adios amigos     Hash  hello   hello world   goodbye   adios amigos       Hash  goodbye   adios amigos   hello   hello world    Hash   hello world     Hash   hello world       Hash   hello world    Hash 1   Hash 1     Hash 1  Hash  1    Hash  1      Hash  1     Output  432700947 true -411117486 true 1725787021 true -1585332251 true 1 true -1881759168 true   Explanation  As you can see the heart of the service is the hash function created by KimKha I have added types to the strings so that the sturucture of the object would also impact the final hash value The keys are hashed to prevent array object collisions   eyelidlessness object comparision is used to prevent infinit recursion by self referencing objects   Usage  I created this service so that I could have an error service that is accessed with objects  So that one service can register an error with a given object and another can determine if any errors were found   ie  JsonValidation js  ErrorSvc  id  1  json    attr   not-valid       Invalid Json Syntax - key not double quoted      UserOfData js  ErrorSvc  id  1  json    attr   not-valid         This would return     Invalid Json Syntax - key not double quoted     While  ErrorSvc  id  1  json     attr    not-valid         This would return

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If you truly want set behavior  I m going by Java knowledge   then you will be hard pressed to find a solution in JavaScript  Most developers will recommend a unique key to represent each object  but this is unlike set  in that you can get two identical objects each with a unique key  The Java API does the work of checking for duplicate values by comparing hash code values  not keys  and since there is no hash code value representation of objects in JavaScript  it becomes almost impossible to do the same  Even the Prototype JS library admits this shortcoming  when it says       Hash can be thought of as an   associative array  binding unique keys   to values  which are not necessarily   unique        http   www prototypejs org api hash

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If you want to use objects as keys you need to overwrite their toString Method  as some already mentioned here  The hash functions that were used are all fine  but they only work for the same objects not for equal objects   I ve written a small library that creates hashes from objects  which you can easily use for this purpose  The objects can even have a different order  the hashes will be the same  Internally you can use different types for your hash  djb2  md5  sha1  sha256  sha512  ripemd160    Here is a small example from the documentation   var hash   require  es-hash        Save data in an object with an object as a key Object prototype toString   function          return   object Object    hash this          var foo        foo  bar   foo       foo          Output      foo     undefined     console log foo  bar   foo      console log foo         The package can be used either in browser and in Node-Js   Repository  https   bitbucket org tehrengruber es-js-hash

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The easiest way to do this is to give each of your objects its own unique toString method    function         var id   0         global MyObject        MyObject   function             this objectId     lt  MyObject      id        gt            this toString  function                 return this objectId                            I had the same problem and this solved it perfectly for me with minimal fuss  and was a lot easier that re-implementing some fatty Java style Hashtable and adding equals   and hashCode   to your object classes  Just make sure that you don t also stick a string   lt  MyObject 12  into your hash or it will wipe out the entry for your exiting object with that id   Now all my hashes are totally chill  I also just posted a blog entry a few days ago about this exact topic

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In addition to eyelidlessness s answer  here is a function that returns a reproducible  unique ID for any object   var uniqueIdList       function getConstantUniqueIdFor element           HACK  using a list results in O n   but how do we hash e g  a DOM node      if  uniqueIdList indexOf element   lt  0            uniqueIdList push element             return uniqueIdList indexOf element       As you can see it uses a list for look-up which is very inefficient  however that s the best I could find for now

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JavaScript objects can only use strings as keys  anything else is converted to a string    You could  alternatively  maintain an array which indexes the objects in question  and use its index string as a reference to the object  Something like this   var ObjectReference       ObjectReference push obj    set  ObjectReference     ObjectReference indexOf obj     true    Obviously it s a little verbose  but you could write a couple of methods that handle it and get and set all willy nilly   Edit      Your guess is fact -- this is defined behaviour in JavaScript -- specifically a toString conversion occurs meaning that you can can define your own toString function on the object that will be used as the property name  - olliej   This brings up another interesting point  you can define a toString method on the objects you want to hash  and that can form their hash identifier

[javascript] Is there any kind of hash code function in JavaScript?

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