How to create dictionary and add key value pairs dynamically

Question

From post   Sending a JSON array to be received as a Dictionary lt string string gt   I   m trying to do this same thing as that post  The only issue is that I don   t know what the keys and the values are upfront  So I need to be able to dynamically add the key and value pairs and I don   t know how to do that   Does anyone know how to create that object and add key value pairs dynamically   I   ve tried   var vars     key  key   value  value     vars 0  key    newkey   vars 0  value    newvalue     But that doesn   t work

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In ES6 you can do this  let cake        let pan        cake              Output - gt              Old Way let cake       let pan       pan cake            Output - gt

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var dict          create an empty array  dict push       key     keyName       value   the value         repeat this last part as needed to add more key value pairs   Basically  you re creating an object literal with 2 properties  called key and value  and inserting it  using push    into the array     Edit  So almost 5 years later  this answer is getting downvotes because it s not creating an  normal  JS object literal  aka map  aka hash  aka dictionary   It is however creating the structure that OP asked for  and which is illustrated in the other question linked to   which is an array of object literals  each with key and value properties  Don t ask me why that structure was required  but it s the one that was asked for   But  but  if what you want in a plain JS object - and not the structure OP asked for - see tcll s answer  though the bracket notation is a bit cumbersome if you just have simple keys that are valid JS names  You can just do this      object literal with properties var dict       key1   value1     key2   value2       etc       Or use regular dot-notation to set properties after creating an object      empty object literal with properties added afterward var dict       dict key1    value1   dict key2    value2      etc    You do want the bracket notation if you ve got keys that have spaces in them  special characters  or things like that  E g   var dict           this obviously won t work dict some invalid key  for multiple reasons     value1       but this will dict  some invalid key  for multiple reasons       value1     You also want bracket notation if your keys are dynamic   dict firstName         lastName     some value     Note that keys  property names  are always strings  and non-string values will be coerced to a string when used as a key  E g  a Date object gets converted to its string representation   dict new Date     today s value    console log dict        gt             Sat Nov 04 2016 16 15 31 GMT-0700  PDT     today s value            Note however that this doesn t necessarily  just work   as many objects will have a string representation like   object Object   which doesn t make for a non-unique key  So be wary of something like   var objA     a  23        objB     b  42     dict objA     value for objA   dict objB     value for objB    console log dict        gt      object Object     value for objB      Despite objA and objB being completely different and unique elements  they both have the same basic string representation    object Object     The reason Date doesn t behave like this is that the Date prototype has a custom toString method which overrides the default string representation  And you can do the same      a simple constructor with a toString prototypal method function Foo       this myRandomNumber   Math random     1000   0     Foo prototype toString   function        return  Foo instance      this myRandomNumber      dict new Foo     some value    console log dict        gt             Foo instance  712    some value             Note that since the above uses a random number  name collisions can still occur very easily  It s just to illustrate an implementation of toString    So when trying to use objects as keys  JS will use the object s own toString implementation  if any  or use the default string representation

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Since you ve stated that you want a dictionary object  and not an array like I assume some understood  I think this is what you are after   var input     key  key1   value  value1    key  key2   value  value2      var result        for var i   0  i  lt  input length  i          result input i  key    input i  value     console log result      Just for testing

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An improvement on var dict      is to use var dict   Object create null    This will create an empty object that does not have Object prototype as it s prototype    var dict1       if  dict1  toString         console log  Hey  I didn t put that there      var dict2   Object create null   if  dict2  toString         console log  This line won t run

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how about the one liner for creating a key value pair   let result       foo     some value       and some iterator function like reduce to dynamically convert an array to a dictionary    x000D   x000D  var options     x000D      key   foo   value  1    x000D      key   bar   value   id  2  name   two      x000D      key   baz   value     active    true     x000D     x000D   x000D  var result   options reduce  accumulator  current    gt    x000D    accumulator current key    current value  x000D    return accumulator  x000D          x000D   x000D  console log result   x000D   x000D   x000D

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I ran into this problem   but within a for loop  The top solution did not work  when using variables  and not strings  for the parameters of the push function   and the others did not account for key values based on variables  I was surprised this approach  which is common in php  worked         example dict json                     var iterateDict     record identifier     content   Some content   title   Title of my Record         record identifier 2     content   Some  different content   title   Title of my another Record         var array             key to reduce the  record  to   var reduceKey    title      for key in iterateDict        ultra-safe variable checking       if iterateDict key      undefined  amp  amp  iterateDict key  reduceKey      undefined         build element to new array key      array key  iterateDict key  reduceKey

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var dictionary        create new object dictionary  key1     value1   set key1 var key1   dictionary  key1     get key1

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In case if someone needs to create a dictionary object dynamically you can use the following code snippet  x000D   x000D     let vars     key  key   value  value    key  key2   value  value2          let dict         vars map varItem  gt                 dict varItem key  varItem value                     console log dict  x000D   x000D   x000D

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var dict        dict  key      testing    console log dict     works just like python     console output   Object  key   testing

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First Initialise Array Globally   var dict           Add Object into Dictionary   dict push         key   One  value  false          key   Two  value  false          key   Three  value  false     Output        0    key    One    value   false      1    key    Two    value   false      2    key    Three    value   false        Update Object from Dictionary      Object keys dict  map  index    gt              if  index    1       dict index  value   true          Output        0    key    One    value   false       1    key    Two    value   true       2    key    Three    value   false        Delete Object from Dictionary   Object keys dict  map  index    gt                        if  index    2           dict splice index                   Output         0    key    One    value   false        1    key    Two    value   true

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Its as simple as   var blah          make a new dictionary  empty    or  var blah    key  value  key2  value2      make a new dictionary with two pairs    then  blah key3   value3     add a new key value pair blah key2     returns value2 blah  key2       also returns value2

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You can use maps with Map  like this   var sayings   new Map    sayings set  dog    woof    sayings set  cat    meow

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JavaScript s Object is in itself like a dictionary  No need to reinvent the wheel   var dict           Adding key-value -pairs dict  key      value      Through indexer dict anotherKey    anotherValue      Through assignment     Looping through for  var item in dict      console log  key     item     value     dict item         Output      key key value value      key anotherKey value anotherValue       Non existent key console log dict notExist      undefined     Contains key  if  dict hasOwnProperty  key           Remove item   delete dict key        Looping through for  var item in dict      console log  key     item     value     dict item         Output      key anotherKey value anotherValue     Fiddle

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You could create a class Dictionary so you can interact with the Dictionary list easily    x000D   x000D  class Dictionary   x000D    constructor     x000D      this items       x000D      x000D    has key    x000D      return key in this items  x000D      x000D    set key value    x000D      this items key    value  x000D      x000D    delete key    x000D      if  this has key     x000D        delete this items key  x000D        return true  x000D        x000D      return false  x000D      x000D    x000D   x000D  var d   new Dictionary    x000D  d set 1   value1   x000D  d set 2   value2   x000D  d set 3   value3   x000D  console log d has 2    x000D  d delete 2   x000D  console log d has 2    x000D   x000D   x000D

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In modern javascript  ES6 ES2015   one should use Map data structure for dictionary  The Map data structure in ES6 lets you use arbitrary values as keys   const map   new Map    map set  true   1   map set  false   0     In you are still using ES5  the correct way to create dictionary is to create object without a prototype in the following way    var map   Object create null   map  true    1  map  false    0    There are many advantages of creating a dictionary without a prototype object  Below blogs are worth reading on this topic   dict-pattern  objects-as-maps

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I happened to walk across this question looking for something similar  It gave me enough info to run a test to get the answer I wanted  So if anyone else wants to know how to dynamically add to or lookup a  key   value   pair in a JavaScript object  this test should tell you all you might need to know    var dictionary    initialkey   initialValue    var key    something   var key2     somethingElse   var value    value1   var value2    value2   var keyInitial    initialkey    console log dictionary keyInitial     dictionary key   value  dictionary key2    value2  console log dictionary     output  initialValue   initialkey   initialValue     something   value1     somethingElse   value2

[javascript] How to create dictionary and add key–value pairs dynamically?

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