Dynamically creating keys in a JavaScript associative array

Question

All the documentation I ve found so far is to update keys that are already created   arr  key     val   I have a string like this   quot  name    oscar  quot   And I want to end up with something like this    name   whatever     That is  split the string and get the first element  and then put that in a dictionary  Code var text     name   oscar   var dict   new Array    var keyValuePair   text split         dict  keyValuePair 0       whatever   alert  dict       Prints nothing

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JavaScript does not have associative arrays  It has objects  The following lines of code all do exactly the same thing - set the  name  field on an object to  orion   var f   new Object    f name    orion   var f   new Object    f  name      orion   var f   new Array    f name    orion   var f   new Array    f  name      orion   var f   new XMLHttpRequest    f  name      orion    It looks like you have an associative array because an Array is also an Object - however you re not actually adding things into the array at all  you re setting fields on the object  Now that that is cleared up  here is a working solution to your example  var text      name   oscar    var dict   new Object        Remove    and spaces var cleaned   text replace        g           Split into key and value var kvp   cleaned split           Put in the object dict  kvp 0      kvp 1   alert  dict name       Prints oscar

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Use the first example   If the key doesn t exist it will be added   var a   new Array    a  name      oscar   alert a  name       Will pop up a message box containing  oscar    Try   var text    name   oscar  var dict   new Array   var keyValuePair   text replace    g     split       dict  keyValuePair 0      keyValuePair 1   alert  dict keyValuePair 0

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Somehow all examples  while work well  are overcomplicated   They use new Array    which is an overkill  and an overhead  for a simple associative array  AKA dictionary   The better ones use new Object    It works fine  but why all this extra typing   This question is tagged  quot beginner quot   so let s make it simple  The   ber-simple way to use a dictionary in JavaScript or  quot Why doesn t JavaScript have a special dictionary object  quot      Create an empty associative array  in JavaScript it is called     Object  var dict            Huh     is a shortcut for  quot new Object   quot      Add a key named fred with value 42 dict fred   42      We can do that because  quot fred quot  is a constant                     and conforms to id rules     Add a key named 2bob2 with value  quot twins  quot  dict  quot 2bob2 quot      quot twins  quot       We use the subscript notation because                               the key is arbitrary  not id      Add an arbitrary dynamic key with a dynamic value var key           Insanely complex calculations for the key     val           Insanely complex calculations for the value dict key    val      Read value of  quot fred quot  val   dict fred      Read value of 2bob2 val   dict  quot 2bob2 quot        Read value of our cool secret key val   dict key    Now let s change values     Change the value of fred dict fred    quot astra quot      The assignment creates and or replaces key-value pairs     Change the value of 2bob2 dict  quot 2bob2 quot      1  2  3       Any legal value can be used     Change value of our secret key dict key    undefined     Contrary to popular beliefs  assigning  quot undefined quot  does not remove the key     Go over all keys and values in our dictionary for  key in dict         A for-in loop goes over all properties  including inherited properties      Let s use only our own properties   if  dict hasOwnProperty key         console log  quot key    quot    key    quot   value    quot    dict key           Deleting values is easy too     Let s delete fred delete dict fred     fred is removed  but the rest is still intact     Let s delete 2bob2 delete dict  quot 2bob2 quot        Let s delete our secret key delete dict key       Now dict is empty     Let s replace it  recreating all original data dict       fred     42     quot 2bob2 quot    quot twins  quot       We can t add the original secret key because it was dynamic  but      we can only add static keys               oh well   temp1    val       Let s rename temp1 into our secret key  if  key     quot temp1 quot       dict key    dict temp1     Copy the value   delete dict temp1          Kill the old key   else        Do nothing  we are good  -

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Somehow all examples  while work well  are overcomplicated   They use new Array    which is an overkill  and an overhead  for a simple associative array  AKA dictionary   The better ones use new Object    It works fine  but why all this extra typing   This question is tagged  quot beginner quot   so let s make it simple  The   ber-simple way to use a dictionary in JavaScript or  quot Why doesn t JavaScript have a special dictionary object  quot      Create an empty associative array  in JavaScript it is called     Object  var dict            Huh     is a shortcut for  quot new Object   quot      Add a key named fred with value 42 dict fred   42      We can do that because  quot fred quot  is a constant                     and conforms to id rules     Add a key named 2bob2 with value  quot twins  quot  dict  quot 2bob2 quot      quot twins  quot       We use the subscript notation because                               the key is arbitrary  not id      Add an arbitrary dynamic key with a dynamic value var key           Insanely complex calculations for the key     val           Insanely complex calculations for the value dict key    val      Read value of  quot fred quot  val   dict fred      Read value of 2bob2 val   dict  quot 2bob2 quot        Read value of our cool secret key val   dict key    Now let s change values     Change the value of fred dict fred    quot astra quot      The assignment creates and or replaces key-value pairs     Change the value of 2bob2 dict  quot 2bob2 quot      1  2  3       Any legal value can be used     Change value of our secret key dict key    undefined     Contrary to popular beliefs  assigning  quot undefined quot  does not remove the key     Go over all keys and values in our dictionary for  key in dict         A for-in loop goes over all properties  including inherited properties      Let s use only our own properties   if  dict hasOwnProperty key         console log  quot key    quot    key    quot   value    quot    dict key           Deleting values is easy too     Let s delete fred delete dict fred     fred is removed  but the rest is still intact     Let s delete 2bob2 delete dict  quot 2bob2 quot        Let s delete our secret key delete dict key       Now dict is empty     Let s replace it  recreating all original data dict       fred     42     quot 2bob2 quot    quot twins  quot       We can t add the original secret key because it was dynamic  but      we can only add static keys               oh well   temp1    val       Let s rename temp1 into our secret key  if  key     quot temp1 quot       dict key    dict temp1     Copy the value   delete dict temp1          Kill the old key   else        Do nothing  we are good  -

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var obj        for  i   0  i  lt  data length  i          if i 2  0            var left   data i  substring data i  indexOf        1           var right   data i   1  substring data i   1  indexOf        1            obj left    right          count             console log  quot obj quot    console log obj       Show the values stored for  var i in obj        console log  key is      i      value is      obj i

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var obj        for  i   0  i  lt  data length  i          if i 2  0            var left   data i  substring data i  indexOf        1           var right   data i   1  substring data i   1  indexOf        1            obj left    right          count             console log  quot obj quot    console log obj       Show the values stored for  var i in obj        console log  key is      i      value is      obj i

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In response to MK Dev  one is able to iterate  but not consecutively  for that  obviously an array is needed   A quick Google search brings up hash tables in JavaScript  Example code for looping over values in a hash  from the aforementioned link   var myArray   new Array    myArray  one     1  myArray  two     2  myArray  three     3      Show the values stored for  var i in myArray        alert  key is      i      value is      myArray i

User · Answer

JavaScript does not have associative arrays  It has objects  The following lines of code all do exactly the same thing - set the  name  field on an object to  orion   var f   new Object    f name    orion   var f   new Object    f  name      orion   var f   new Array    f name    orion   var f   new Array    f  name      orion   var f   new XMLHttpRequest    f  name      orion    It looks like you have an associative array because an Array is also an Object - however you re not actually adding things into the array at all  you re setting fields on the object  Now that that is cleared up  here is a working solution to your example  var text      name   oscar    var dict   new Object        Remove    and spaces var cleaned   text replace        g           Split into key and value var kvp   cleaned split           Put in the object dict  kvp 0      kvp 1   alert  dict name       Prints oscar

User · Answer

Somehow all examples  while work well  are overcomplicated   They use new Array    which is an overkill  and an overhead  for a simple associative array  AKA dictionary   The better ones use new Object    It works fine  but why all this extra typing   This question is tagged  quot beginner quot   so let s make it simple  The   ber-simple way to use a dictionary in JavaScript or  quot Why doesn t JavaScript have a special dictionary object  quot      Create an empty associative array  in JavaScript it is called     Object  var dict            Huh     is a shortcut for  quot new Object   quot      Add a key named fred with value 42 dict fred   42      We can do that because  quot fred quot  is a constant                     and conforms to id rules     Add a key named 2bob2 with value  quot twins  quot  dict  quot 2bob2 quot      quot twins  quot       We use the subscript notation because                               the key is arbitrary  not id      Add an arbitrary dynamic key with a dynamic value var key           Insanely complex calculations for the key     val           Insanely complex calculations for the value dict key    val      Read value of  quot fred quot  val   dict fred      Read value of 2bob2 val   dict  quot 2bob2 quot        Read value of our cool secret key val   dict key    Now let s change values     Change the value of fred dict fred    quot astra quot      The assignment creates and or replaces key-value pairs     Change the value of 2bob2 dict  quot 2bob2 quot      1  2  3       Any legal value can be used     Change value of our secret key dict key    undefined     Contrary to popular beliefs  assigning  quot undefined quot  does not remove the key     Go over all keys and values in our dictionary for  key in dict         A for-in loop goes over all properties  including inherited properties      Let s use only our own properties   if  dict hasOwnProperty key         console log  quot key    quot    key    quot   value    quot    dict key           Deleting values is easy too     Let s delete fred delete dict fred     fred is removed  but the rest is still intact     Let s delete 2bob2 delete dict  quot 2bob2 quot        Let s delete our secret key delete dict key       Now dict is empty     Let s replace it  recreating all original data dict       fred     42     quot 2bob2 quot    quot twins  quot       We can t add the original secret key because it was dynamic  but      we can only add static keys               oh well   temp1    val       Let s rename temp1 into our secret key  if  key     quot temp1 quot       dict key    dict temp1     Copy the value   delete dict temp1          Kill the old key   else        Do nothing  we are good  -

User · Answer

In response to MK Dev  one is able to iterate  but not consecutively  for that  obviously an array is needed   A quick Google search brings up hash tables in JavaScript  Example code for looping over values in a hash  from the aforementioned link   var myArray   new Array    myArray  one     1  myArray  two     2  myArray  three     3      Show the values stored for  var i in myArray        alert  key is      i      value is      myArray i

User · Answer

JavaScript does not have associative arrays  It has objects  The following lines of code all do exactly the same thing - set the  name  field on an object to  orion   var f   new Object    f name    orion   var f   new Object    f  name      orion   var f   new Array    f name    orion   var f   new Array    f  name      orion   var f   new XMLHttpRequest    f  name      orion    It looks like you have an associative array because an Array is also an Object - however you re not actually adding things into the array at all  you re setting fields on the object  Now that that is cleared up  here is a working solution to your example  var text      name   oscar    var dict   new Object        Remove    and spaces var cleaned   text replace        g           Split into key and value var kvp   cleaned split           Put in the object dict  kvp 0      kvp 1   alert  dict name       Prints oscar

User · Answer

Use the first example   If the key doesn t exist it will be added   var a   new Array    a  name      oscar   alert a  name       Will pop up a message box containing  oscar    Try   var text    name   oscar  var dict   new Array   var keyValuePair   text replace    g     split       dict  keyValuePair 0      keyValuePair 1   alert  dict keyValuePair 0

User · Answer

The original code  I added the line numbers so can refer to them   1  var text     name   oscar   2  var dict   new Array    3  var keyValuePair   text split         4  dict  keyValuePair 0       whatever   5  alert  dict       Prints nothing   Almost there     line 1  you should do a trim on text so it is name   oscar   line 3  okay as long as you always have spaces around your equal  It might be better to not trim in line 1  Use   and trim each keyValuePair  add a line after 3 and before 4    key   keyValuePair 0      line 4  Now becomes    dict key    keyValuePair 1     line 5  Change to    alert  dict  name          It will print out  oscar     I m trying to say that the dict keyValuePair 0   does not work  You need to set a string to keyValuePair 0  and use that as the associative key  That is the only way I got mine to work  After you have set it up  you can either refer to it with numeric index or key in quotes

User · Answer

The original code  I added the line numbers so can refer to them   1  var text     name   oscar   2  var dict   new Array    3  var keyValuePair   text split         4  dict  keyValuePair 0       whatever   5  alert  dict       Prints nothing   Almost there     line 1  you should do a trim on text so it is name   oscar   line 3  okay as long as you always have spaces around your equal  It might be better to not trim in line 1  Use   and trim each keyValuePair  add a line after 3 and before 4    key   keyValuePair 0      line 4  Now becomes    dict key    keyValuePair 1     line 5  Change to    alert  dict  name          It will print out  oscar     I m trying to say that the dict keyValuePair 0   does not work  You need to set a string to keyValuePair 0  and use that as the associative key  That is the only way I got mine to work  After you have set it up  you can either refer to it with numeric index or key in quotes

User · Answer

Use the first example   If the key doesn t exist it will be added   var a   new Array    a  name      oscar   alert a  name       Will pop up a message box containing  oscar    Try   var text    name   oscar  var dict   new Array   var keyValuePair   text replace    g     split       dict  keyValuePair 0      keyValuePair 1   alert  dict keyValuePair 0

User · Answer

In response to MK Dev  one is able to iterate  but not consecutively  for that  obviously an array is needed   A quick Google search brings up hash tables in JavaScript  Example code for looping over values in a hash  from the aforementioned link   var myArray   new Array    myArray  one     1  myArray  two     2  myArray  three     3      Show the values stored for  var i in myArray        alert  key is      i      value is      myArray i

User · Answer

Somehow all examples  while work well  are overcomplicated   They use new Array    which is an overkill  and an overhead  for a simple associative array  AKA dictionary   The better ones use new Object    It works fine  but why all this extra typing   This question is tagged  quot beginner quot   so let s make it simple  The   ber-simple way to use a dictionary in JavaScript or  quot Why doesn t JavaScript have a special dictionary object  quot      Create an empty associative array  in JavaScript it is called     Object  var dict            Huh     is a shortcut for  quot new Object   quot      Add a key named fred with value 42 dict fred   42      We can do that because  quot fred quot  is a constant                     and conforms to id rules     Add a key named 2bob2 with value  quot twins  quot  dict  quot 2bob2 quot      quot twins  quot       We use the subscript notation because                               the key is arbitrary  not id      Add an arbitrary dynamic key with a dynamic value var key           Insanely complex calculations for the key     val           Insanely complex calculations for the value dict key    val      Read value of  quot fred quot  val   dict fred      Read value of 2bob2 val   dict  quot 2bob2 quot        Read value of our cool secret key val   dict key    Now let s change values     Change the value of fred dict fred    quot astra quot      The assignment creates and or replaces key-value pairs     Change the value of 2bob2 dict  quot 2bob2 quot      1  2  3       Any legal value can be used     Change value of our secret key dict key    undefined     Contrary to popular beliefs  assigning  quot undefined quot  does not remove the key     Go over all keys and values in our dictionary for  key in dict         A for-in loop goes over all properties  including inherited properties      Let s use only our own properties   if  dict hasOwnProperty key         console log  quot key    quot    key    quot   value    quot    dict key           Deleting values is easy too     Let s delete fred delete dict fred     fred is removed  but the rest is still intact     Let s delete 2bob2 delete dict  quot 2bob2 quot        Let s delete our secret key delete dict key       Now dict is empty     Let s replace it  recreating all original data dict       fred     42     quot 2bob2 quot    quot twins  quot       We can t add the original secret key because it was dynamic  but      we can only add static keys               oh well   temp1    val       Let s rename temp1 into our secret key  if  key     quot temp1 quot       dict key    dict temp1     Copy the value   delete dict temp1          Kill the old key   else        Do nothing  we are good  -

User · Answer

I think it is better if you just created it like this  var arr        arr        key1   value1      key2  value2      For more info  take a look at this  JavaScript Data Structures - Associative Array

User · Answer

var myArray   new Array    myArray  one     1  myArray  two     2  myArray  three     3      Show the values stored for  var i in myArray        alert  key is      i      value is      myArray i       This is ok  but it iterates through every property of the array object  If you want to only iterate through the properties myArray one  myArray two    you try like this  myArray  one     1  myArray  two     2  myArray  three     3  myArray push  quot one quot    myArray push  quot two quot    myArray push  quot three quot    for var i 0 i lt maArray length i         console log myArray myArray i       Now you can access both by myArray  quot one quot   and iterate only through these properties

User · Answer

In response to MK Dev  one is able to iterate  but not consecutively  for that  obviously an array is needed   A quick Google search brings up hash tables in JavaScript  Example code for looping over values in a hash  from the aforementioned link   var myArray   new Array    myArray  one     1  myArray  two     2  myArray  three     3      Show the values stored for  var i in myArray        alert  key is      i      value is      myArray i

User · Answer

I think it is better if you just created it like this  var arr        arr        key1   value1      key2  value2      For more info  take a look at this  JavaScript Data Structures - Associative Array

User · Answer

All modern browsers support a Map  which is a key value data structure  There are a couple of reasons that make using a Map better than Object    An Object has a prototype  so there are default keys in the map  The keys of an Object are strings  where they can be any value for a Map  You can get the size of a Map easily while you have to keep track of size for an Object    Example  var myMap   new Map     var keyObj           keyFunc   function            keyString    quot a string quot    myMap set keyString   quot value associated with  a string  quot    myMap set keyObj   quot value associated with keyObj quot    myMap set keyFunc   quot value associated with keyFunc quot     myMap size     3  myMap get keyString          quot value associated with  a string  quot  myMap get keyObj             quot value associated with keyObj quot  myMap get keyFunc            quot value associated with keyFunc quot   If you want keys that are not referenced from other objects to be garbage collected  consider using a WeakMap instead of a Map

User · Answer

All modern browsers support a Map  which is a key value data structure  There are a couple of reasons that make using a Map better than Object    An Object has a prototype  so there are default keys in the map  The keys of an Object are strings  where they can be any value for a Map  You can get the size of a Map easily while you have to keep track of size for an Object    Example  var myMap   new Map     var keyObj           keyFunc   function            keyString    quot a string quot    myMap set keyString   quot value associated with  a string  quot    myMap set keyObj   quot value associated with keyObj quot    myMap set keyFunc   quot value associated with keyFunc quot     myMap size     3  myMap get keyString          quot value associated with  a string  quot  myMap get keyObj             quot value associated with keyObj quot  myMap get keyFunc            quot value associated with keyFunc quot   If you want keys that are not referenced from other objects to be garbage collected  consider using a WeakMap instead of a Map

User · Answer

JavaScript does not have associative arrays  It has objects  The following lines of code all do exactly the same thing - set the  name  field on an object to  orion   var f   new Object    f name    orion   var f   new Object    f  name      orion   var f   new Array    f name    orion   var f   new Array    f  name      orion   var f   new XMLHttpRequest    f  name      orion    It looks like you have an associative array because an Array is also an Object - however you re not actually adding things into the array at all  you re setting fields on the object  Now that that is cleared up  here is a working solution to your example  var text      name   oscar    var dict   new Object        Remove    and spaces var cleaned   text replace        g           Split into key and value var kvp   cleaned split           Put in the object dict  kvp 0      kvp 1   alert  dict name       Prints oscar

User · Answer

var myArray   new Array    myArray  one     1  myArray  two     2  myArray  three     3      Show the values stored for  var i in myArray        alert  key is      i      value is      myArray i       This is ok  but it iterates through every property of the array object  If you want to only iterate through the properties myArray one  myArray two    you try like this  myArray  one     1  myArray  two     2  myArray  three     3  myArray push  quot one quot    myArray push  quot two quot    myArray push  quot three quot    for var i 0 i lt maArray length i         console log myArray myArray i       Now you can access both by myArray  quot one quot   and iterate only through these properties

User · Answer

Use the first example   If the key doesn t exist it will be added   var a   new Array    a  name      oscar   alert a  name       Will pop up a message box containing  oscar    Try   var text    name   oscar  var dict   new Array   var keyValuePair   text replace    g     split       dict  keyValuePair 0      keyValuePair 1   alert  dict keyValuePair 0

[javascript] Dynamically creating keys in a JavaScript associative array

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