How do I remove objects from a JavaScript associative array

Question

Suppose I have this code  var myArray   new Object    myArray  quot firstname quot      quot Bob quot   myArray  quot lastname quot      quot Smith quot   myArray  quot age quot     25   Now if I wanted to remove  quot lastname quot      is there some equivalent of myArray  quot lastname quot   remove     I need the element gone because the number of elements is important and I want to keep things clean

User · Answer

You can remove an entry from your map by explicitly assigning it to  undefined   As in your case      myArray  lastname     undefined

User · Answer

By using the  quot delete quot  keyword  it will delete the array element from array in JavaScript  For example  Consider following statements  var arrayElementToDelete   new Object     arrayElementToDelete  quot id quot                quot XERTYB00G1 quot   arrayElementToDelete  quot first name quot        quot Employee one quot   arrayElementToDelete  quot status quot            quot Active quot    delete arrayElementToDelete  quot status quot     The last line of the code will remove the array element whose key is  quot status quot  from the array

User · Answer

Use method splice to completely remove an item from an object array  Object prototype removeItem   function  key  value        if  value    undefined          return       for  var i in this            if  this i  key     value                this splice i  1                       var collection           id   quot 5f299a5d-7793-47be-a827-bca227dbef95 quot   title   quot one quot           id   quot 87353080-8f49-46b9-9281-162a41ddb8df quot   title   quot two quot           id   quot a1af832c-9028-4690-9793-d623ecc75a95 quot   title   quot three quot        collection removeItem  quot id quot    quot 87353080-8f49-46b9-9281-162a41ddb8df quot

User · Answer

None of the previous answers address the fact that JavaScript does not have associative arrays to begin with - there is no array type as such  see typeof  What JavaScript has  are object instances with dynamic properties  When properties are confused with elements of an Array object instance then Bad Things    are bound to happen  Problem var elements   new Array    elements push document getElementsByTagName  quot head quot   0   elements push document getElementsByTagName  quot title quot   0   elements  quot prop quot     document getElementsByTagName  quot body quot   0   console log  quot number of elements   quot   elements length       Returns 2 delete elements 1  console log  quot number of elements   quot   elements length       Returns 2       for  var i   0  i  lt  elements length  i            Uh-oh    throws a TypeError when i    1    elements i  onmouseover   function      window alert  quot Over It  quot       console log  quot success at index   quot   i     Solution To have a universal removal function that does not blow up on you  use  Object prototype removeItem   function  key       if   this hasOwnProperty key         return    if  isNaN parseInt key        this instanceof Array         delete this key     else       this splice key  1            Code sample     var elements   new Array    elements push document getElementsByTagName  quot head quot   0   elements push document getElementsByTagName  quot title quot   0   elements  quot prop quot     document getElementsByTagName  quot body quot   0   console log elements length                            Returns 2 elements removeItem  quot prop quot   elements removeItem 0  console log elements hasOwnProperty  quot prop quot              Returns false as it should console log elements length                            returns 1 as it should

User · Answer

Objects in JavaScript can be thought of as associative arrays  mapping keys  properties  to values   To remove a property from an object in JavaScript you use the delete operator   const o     lastName   foo    o hasOwnProperty  lastName      true delete o  lastName   o hasOwnProperty  lastName      false   Note that when delete is applied to an index property of an Array  you will create a sparsely populated array  ie  an array with a missing index    When working with instances of Array  if you do not want to create a sparsely populated array - and you usually don t - then you should use Array splice or Array pop   Note that the delete operator in JavaScript does not directly free memory  Its purpose is to remove properties from objects  Of course  if a property being deleted holds the only remaining reference to an object o  then o will subsequently be garbage collected in the normal way   Using the delete operator can affect JavaScript engines  ability to optimise code

User · Answer

All objects in JavaScript are implemented as hashtables associative arrays  So  the following are the equivalent   alert myObj  SomeProperty     alert myObj SomeProperty     And  as already indicated  you  remove  a property from an object via the delete keyword  which you can use in two ways   delete myObj  SomeProperty    delete myObj SomeProperty    Hope the extra info helps

User · Answer

The only working method for me  function removeItem  array  value        var i   0      while  i  lt  array length            if array i      value                array splice i  1             else                 i                      return array     Usage  var new   removeItem    quot apple quot   quot banana quot    quot orange quot      quot apple quot       --- gt    quot banana quot    quot orange quot

User · Answer

Objects in JavaScript can be thought of as associative arrays  mapping keys  properties  to values   To remove a property from an object in JavaScript you use the delete operator   const o     lastName   foo    o hasOwnProperty  lastName      true delete o  lastName   o hasOwnProperty  lastName      false   Note that when delete is applied to an index property of an Array  you will create a sparsely populated array  ie  an array with a missing index    When working with instances of Array  if you do not want to create a sparsely populated array - and you usually don t - then you should use Array splice or Array pop   Note that the delete operator in JavaScript does not directly free memory  Its purpose is to remove properties from objects  Of course  if a property being deleted holds the only remaining reference to an object o  then o will subsequently be garbage collected in the normal way   Using the delete operator can affect JavaScript engines  ability to optimise code

User · Answer

None of the previous answers address the fact that JavaScript does not have associative arrays to begin with - there is no array type as such  see typeof  What JavaScript has  are object instances with dynamic properties  When properties are confused with elements of an Array object instance then Bad Things    are bound to happen  Problem var elements   new Array    elements push document getElementsByTagName  quot head quot   0   elements push document getElementsByTagName  quot title quot   0   elements  quot prop quot     document getElementsByTagName  quot body quot   0   console log  quot number of elements   quot   elements length       Returns 2 delete elements 1  console log  quot number of elements   quot   elements length       Returns 2       for  var i   0  i  lt  elements length  i            Uh-oh    throws a TypeError when i    1    elements i  onmouseover   function      window alert  quot Over It  quot       console log  quot success at index   quot   i     Solution To have a universal removal function that does not blow up on you  use  Object prototype removeItem   function  key       if   this hasOwnProperty key         return    if  isNaN parseInt key        this instanceof Array         delete this key     else       this splice key  1            Code sample     var elements   new Array    elements push document getElementsByTagName  quot head quot   0   elements push document getElementsByTagName  quot title quot   0   elements  quot prop quot     document getElementsByTagName  quot body quot   0   console log elements length                            Returns 2 elements removeItem  quot prop quot   elements removeItem 0  console log elements hasOwnProperty  quot prop quot              Returns false as it should console log elements length                            returns 1 as it should

User · Answer

By using the  quot delete quot  keyword  it will delete the array element from array in JavaScript  For example  Consider following statements  var arrayElementToDelete   new Object     arrayElementToDelete  quot id quot                quot XERTYB00G1 quot   arrayElementToDelete  quot first name quot        quot Employee one quot   arrayElementToDelete  quot status quot            quot Active quot    delete arrayElementToDelete  quot status quot     The last line of the code will remove the array element whose key is  quot status quot  from the array

User · Answer

It s very straightforward if you have an Underscore js dependency in your project -   omit myArray   quot lastname quot

User · Answer

There is an elegant way in the Airbnb Style Guide to do this  ECMAScript  7   const myObject       a  1    b  2    c  3    const   a     noA     myObject  console log noA        gt    b  2  c  3    Copyright  https   codeburst io use-es2015-object-rest-operator-to-omit-properties-38a3ecffe90

User · Answer

var myArray   newmyArray   new Object    myArray  quot firstname quot      quot Bob quot   myArray  quot lastname quot      quot Smith quot   myArray  quot age quot     25   var s   JSON stringify myArray    s replace   quot lastname        g       newmyArray   JSON parse p    Without looping iterates we get the same result

User · Answer

You are using Object  and you don t have an associative array to begin with  With an associative array  adding and removing items goes like this      Array prototype contains   function obj                var i   this length          while  i--                        if  this i      obj                                return true                                  return false              Array prototype add   function key  value                if this contains key               this key    value          else                       this push key               this key    value                        Array prototype remove   function key                for var i   0  i  lt  this length    i                        if this i     key                                this splice i  1                   return                                          Read a page s GET URL variables and return them as an associative array      function getUrlVars                 var vars       hash          var hashes   window location href slice window location href indexOf        1  split   amp              for var i   0  i  lt  hashes length  i                          hash   hashes i  split                   vars push hash 0                vars hash 0     hash 1                      return vars              function ForwardAndHideVariables             var dictParameters   getUrlVars             dictParameters add  quot mno quot    quot pqr quot            dictParameters add  quot mno quot    quot stfu quot             dictParameters remove  quot mno quot              for var i   0  i  lt  dictParameters length  i                          var key   dictParameters i               var value   dictParameters key               alert key    quot   quot    value                        And now forward with HTTP-POST         aa post to url  quot Default aspx quot   dictParameters               function aa post to url path  params  method            method   method     quot post quot            var form   document createElement  quot form quot                Move the submit function to another variable            so that it doesn t get written over if a parameter name is  submit          form  submit function    form submit           form setAttribute  quot method quot   method           form setAttribute  quot action quot   path            for var i   0  i  lt  params length  i                          var key   params i                var hiddenField   document createElement  quot input quot                hiddenField setAttribute  quot type quot    quot hidden quot                hiddenField setAttribute  quot name quot   key               hiddenField setAttribute  quot value quot   params key                 form appendChild hiddenField                      document body appendChild form           form  submit function        Call the renamed function

User · Answer

All objects in JavaScript are implemented as hashtables associative arrays  So  the following are the equivalent   alert myObj  SomeProperty     alert myObj SomeProperty     And  as already indicated  you  remove  a property from an object via the delete keyword  which you can use in two ways   delete myObj  SomeProperty    delete myObj SomeProperty    Hope the extra info helps

User · Answer

Objects in JavaScript can be thought of as associative arrays  mapping keys  properties  to values   To remove a property from an object in JavaScript you use the delete operator   const o     lastName   foo    o hasOwnProperty  lastName      true delete o  lastName   o hasOwnProperty  lastName      false   Note that when delete is applied to an index property of an Array  you will create a sparsely populated array  ie  an array with a missing index    When working with instances of Array  if you do not want to create a sparsely populated array - and you usually don t - then you should use Array splice or Array pop   Note that the delete operator in JavaScript does not directly free memory  Its purpose is to remove properties from objects  Of course  if a property being deleted holds the only remaining reference to an object o  then o will subsequently be garbage collected in the normal way   Using the delete operator can affect JavaScript engines  ability to optimise code

User · Answer

For  quot Arrays quot   If you know the index  array splice index  1    If you know the value  function removeItem array  value        var index   array indexOf value       if  index  gt  -1            array splice index  1             return array     The most upvoted answer for delete works well in case of objects but not for the real arrays  If I use delete it removes elements from loops but keeps the element as empty and length of array wont change  This may be a problem in some scenarios  For example  if I do myArray toString   on myArray after removal via delete  it creates an empty entry  i e

User · Answer

We can use it as a function too  Angular throws some error if used as a prototype  Thanks  HarpyWar  It helped me solve a problem   var removeItem   function  object  key  value        if  value    undefined          return       for  var i in object            if  object i  key     value                object splice i  1                       var collection           id   5f299a5d-7793-47be-a827-bca227dbef95   title   one           id   87353080-8f49-46b9-9281-162a41ddb8df   title   two           id   a1af832c-9028-4690-9793-d623ecc75a95   title   three        removeItem collection   id    87353080-8f49-46b9-9281-162a41ddb8df

User · Answer

Objects in JavaScript can be thought of as associative arrays  mapping keys  properties  to values   To remove a property from an object in JavaScript you use the delete operator   const o     lastName   foo    o hasOwnProperty  lastName      true delete o  lastName   o hasOwnProperty  lastName      false   Note that when delete is applied to an index property of an Array  you will create a sparsely populated array  ie  an array with a missing index    When working with instances of Array  if you do not want to create a sparsely populated array - and you usually don t - then you should use Array splice or Array pop   Note that the delete operator in JavaScript does not directly free memory  Its purpose is to remove properties from objects  Of course  if a property being deleted holds the only remaining reference to an object o  then o will subsequently be garbage collected in the normal way   Using the delete operator can affect JavaScript engines  ability to optimise code

User · Answer

For  quot Arrays quot   If you know the index  array splice index  1    If you know the value  function removeItem array  value        var index   array indexOf value       if  index  gt  -1            array splice index  1             return array     The most upvoted answer for delete works well in case of objects but not for the real arrays  If I use delete it removes elements from loops but keeps the element as empty and length of array wont change  This may be a problem in some scenarios  For example  if I do myArray toString   on myArray after removal via delete  it creates an empty entry  i e

User · Answer

Use method splice to completely remove an item from an object array  Object prototype removeItem   function  key  value        if  value    undefined          return       for  var i in this            if  this i  key     value                this splice i  1                       var collection           id   quot 5f299a5d-7793-47be-a827-bca227dbef95 quot   title   quot one quot           id   quot 87353080-8f49-46b9-9281-162a41ddb8df quot   title   quot two quot           id   quot a1af832c-9028-4690-9793-d623ecc75a95 quot   title   quot three quot        collection removeItem  quot id quot    quot 87353080-8f49-46b9-9281-162a41ddb8df quot

User · Answer

That only deletes the object  but it still keeps the array length the same  To remove the element from the array  you need to do something like  array splice index  1

User · Answer

While the accepted answer is correct  it is missing the explanation why it works  First of all  your code should reflect the fact that this is not an array  var myObject   new Object    myObject  quot firstname quot      quot Bob quot   myObject  quot lastname quot      quot Smith quot   myObject  quot age quot     25   Note that all objects  including Arrays  can be used this way  However  do not expect for standard JavaScript array functions  pop  push  etc   to work on objects  As said in accepted answer  you can then use delete to remove the entries from objects  delete myObject  quot lastname quot    You should decide which route you wish to take - either use objects  associative arrays   dictionaries  or use arrays  maps   Never mix the two of them

User · Answer

As other answers have noted  you are not using a JavaScript array  but a JavaScript object  which works almost like an associative array in other languages except that all keys are converted to strings  The new Map stores keys as their original type  If you had an array and not an object  you could use the array s  filter function  to return a new array without the item you want removed  var myArray     Bob    Smith   25   myArray   myArray filter function item        return item      Smith        If you have an older browser and jQuery  jQuery has a   grep method that works similarly  myArray     grep myArray  function item        return item      Smith

User · Answer

While the accepted answer is correct  it is missing the explanation why it works  First of all  your code should reflect the fact that this is not an array  var myObject   new Object    myObject  quot firstname quot      quot Bob quot   myObject  quot lastname quot      quot Smith quot   myObject  quot age quot     25   Note that all objects  including Arrays  can be used this way  However  do not expect for standard JavaScript array functions  pop  push  etc   to work on objects  As said in accepted answer  you can then use delete to remove the entries from objects  delete myObject  quot lastname quot    You should decide which route you wish to take - either use objects  associative arrays   dictionaries  or use arrays  maps   Never mix the two of them

User · Answer

All objects in JavaScript are implemented as hashtables associative arrays  So  the following are the equivalent   alert myObj  SomeProperty     alert myObj SomeProperty     And  as already indicated  you  remove  a property from an object via the delete keyword  which you can use in two ways   delete myObj  SomeProperty    delete myObj SomeProperty    Hope the extra info helps

User · Answer

We can use it as a function too  Angular throws some error if used as a prototype  Thanks  HarpyWar  It helped me solve a problem   var removeItem   function  object  key  value        if  value    undefined          return       for  var i in object            if  object i  key     value                object splice i  1                       var collection           id   5f299a5d-7793-47be-a827-bca227dbef95   title   one           id   87353080-8f49-46b9-9281-162a41ddb8df   title   two           id   a1af832c-9028-4690-9793-d623ecc75a95   title   three        removeItem collection   id    87353080-8f49-46b9-9281-162a41ddb8df

User · Answer

You are using Object  and you don t have an associative array to begin with  With an associative array  adding and removing items goes like this      Array prototype contains   function obj                var i   this length          while  i--                        if  this i      obj                                return true                                  return false              Array prototype add   function key  value                if this contains key               this key    value          else                       this push key               this key    value                        Array prototype remove   function key                for var i   0  i  lt  this length    i                        if this i     key                                this splice i  1                   return                                          Read a page s GET URL variables and return them as an associative array      function getUrlVars                 var vars       hash          var hashes   window location href slice window location href indexOf        1  split   amp              for var i   0  i  lt  hashes length  i                          hash   hashes i  split                   vars push hash 0                vars hash 0     hash 1                      return vars              function ForwardAndHideVariables             var dictParameters   getUrlVars             dictParameters add  quot mno quot    quot pqr quot            dictParameters add  quot mno quot    quot stfu quot             dictParameters remove  quot mno quot              for var i   0  i  lt  dictParameters length  i                          var key   dictParameters i               var value   dictParameters key               alert key    quot   quot    value                        And now forward with HTTP-POST         aa post to url  quot Default aspx quot   dictParameters               function aa post to url path  params  method            method   method     quot post quot            var form   document createElement  quot form quot                Move the submit function to another variable            so that it doesn t get written over if a parameter name is  submit          form  submit function    form submit           form setAttribute  quot method quot   method           form setAttribute  quot action quot   path            for var i   0  i  lt  params length  i                          var key   params i                var hiddenField   document createElement  quot input quot                hiddenField setAttribute  quot type quot    quot hidden quot                hiddenField setAttribute  quot name quot   key               hiddenField setAttribute  quot value quot   params key                 form appendChild hiddenField                      document body appendChild form           form  submit function        Call the renamed function

User · Answer

The only working method for me  function removeItem  array  value        var i   0      while  i  lt  array length            if array i      value                array splice i  1             else                 i                      return array     Usage  var new   removeItem    quot apple quot   quot banana quot    quot orange quot      quot apple quot       --- gt    quot banana quot    quot orange quot

User · Answer

If  for whatever reason  the delete key is not working  like it wasn t working for me   you can splice it out and then filter the undefined values     To cut out one element via arr splice indexToRemove  numberToRemove   array splice key  1  array filter function n  return n     Don   t try and chain them since splice returns removed elements

User · Answer

You can remove an entry from your map by explicitly assigning it to  undefined   As in your case      myArray  lastname     undefined

User · Answer

As other answers have noted  you are not using a JavaScript array  but a JavaScript object  which works almost like an associative array in other languages except that all keys are converted to strings  The new Map stores keys as their original type  If you had an array and not an object  you could use the array s  filter function  to return a new array without the item you want removed  var myArray     Bob    Smith   25   myArray   myArray filter function item        return item      Smith        If you have an older browser and jQuery  jQuery has a   grep method that works similarly  myArray     grep myArray  function item        return item      Smith

User · Answer

var myArray   newmyArray   new Object    myArray  quot firstname quot      quot Bob quot   myArray  quot lastname quot      quot Smith quot   myArray  quot age quot     25   var s   JSON stringify myArray    s replace   quot lastname        g       newmyArray   JSON parse p    Without looping iterates we get the same result

User · Answer

If  for whatever reason  the delete key is not working  like it wasn t working for me   you can splice it out and then filter the undefined values     To cut out one element via arr splice indexToRemove  numberToRemove   array splice key  1  array filter function n  return n     Don   t try and chain them since splice returns removed elements

User · Answer

All objects in JavaScript are implemented as hashtables associative arrays  So  the following are the equivalent   alert myObj  SomeProperty     alert myObj SomeProperty     And  as already indicated  you  remove  a property from an object via the delete keyword  which you can use in two ways   delete myObj  SomeProperty    delete myObj SomeProperty    Hope the extra info helps

User · Answer

There is an elegant way in the Airbnb Style Guide to do this  ECMAScript  7   const myObject       a  1    b  2    c  3    const   a     noA     myObject  console log noA        gt    b  2  c  3    Copyright  https   codeburst io use-es2015-object-rest-operator-to-omit-properties-38a3ecffe90

User · Answer

It s very straightforward if you have an Underscore js dependency in your project -   omit myArray   quot lastname quot

User · Answer

That only deletes the object  but it still keeps the array length the same  To remove the element from the array  you need to do something like  array splice index  1

[javascript] How do I remove objects from a JavaScript associative array?

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