Use dynamic variable names in JavaScript

Question

In PHP you can do amazing horrendous things like this    a   1   b   2   c   3   name    a   echo   name     prints 1   Is there any way of doing something like this with Javascript   E g  if I have a var name    the name of the variable   can I get a reference to the variable with name name

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what they mean is no  you can t  there is no way to get it done  so it was possible you could do something like this  function create obj  const      where obj is an object and const is a variable name function const        const prototype myProperty   property value        more prototype  return new const         having a create function just like the one implemented in ECMAScript 5

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This is an alternative for those who need to export a dynamically named variable  export      someVariable    some value      anotherVariable    another value         then     import from another file like this  import   as vars from    some-file    Another alternative is to simply create an object whose keys are named dynamically  const vars      someVariable   1   otherVariable   2        consume it like this vars someVariable

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This will do exactly what you done in php  var a   1  var b   2  var ccc   3  var name    a   console log  window name        1

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It is always better to use create a namespace and declare a variable in it instead of adding it to the global object  We can also create a function to get and set the value See the below code snippet    creating a namespace in which all the variables will be defined  var myObjects        function that will set the name property in the myObjects namespace function setName val     myObjects Name val       function that will return the name property in the myObjects namespace function getName      return myObjects Name       now we can use it like    setName  quot kevin quot      var x   getName      var y   x    console log y      quot kevin quot    var z    quot y quot     console log z      quot y quot    console log eval z       quot kevin quot   In this similar way  we can declare and use multiple variables  Although this will increase the line of code but the code will be more robust and less error-prone

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In Javascript you can use the fact that all properties are key value pairs  jAndy already mentioned this but I don t think his answer show how it can be exploited   Usually you are not trying to create a variable to hold a variable name but are trying to generate variable names and then use them  PHP does it with   var notation but Javascript doesn t need to because property keys are interchangeable with array keys   var id    abc   var mine       mine id    123  console log mine abc     gives 123  Usually you want to construct the variable which is why there is the indirection so you can also do it the other way around   var mine       mine abc   123  console log mine  a   bc

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If you don t want to use a global object like window or global  node   you can try something like this   var obj       obj  whatever      There  s no need to store even more stuff in a global object     console log obj  whatever

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eval is one option   var a   1  var name    a    document write eval name       1

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You can use the window object to get at it     window  myVar     window has a reference to all global variables and global functions you are using

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I needed to draw multiple FormData on the fly and object way worked well  var forms        Then in my loops whereever i needed to create a form data i used  forms  formdata  counter  new FormData    forms  formdata  counter  append var name  var value

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2019   TL DR   eval operator can run string expression in the context it called and return variables from that context   literal object theoretically can do that by write   varName    but it blocked by definition     So I come across this question and everyone here just play around without bringing a real solution  but  Axel Heider has a good approaching   The solution is eval  almost most forgotten operator    think most one is with       eval operator can dynamically run expression in the context it called  and return the result of that expression  we can use that to dynamically return a  variable s value in function s context    example   function exmaple1       var a   1  b   2  default   3     var name    a      return eval name     example1      return 1   function example2 option     var a   1  b   2  defaultValue   3     switch option       case  a   name    a   break      case  b   name    b   break      default  name    defaultValue         return eval  name      example2  a      return 1 example2  b      return 2 example2      return 3   Note that I always write explicitly the expression eval will run  To avoid unnecessary surprises in the code  eval is very strong But I m sure you know that already  BTW  if it was legal we could use literal object to capture the variable name and value  but we can   t combine computed property names and property value shorthand  sadly  is invalid  functopn example  varName        var var1    foo   var2   bar       var capture     varName       example  var1     trow  Uncaught SyntaxError  Unexpected token

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a    varname   str   a        123   eval str  alert varname     Try this

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This is an example     for var i 0  i lt  3  i          window  p  i     hello     i     alert p0      hello 0 alert p1      hello 1 alert p2      hello 2 alert p3      hello 3   Another example    var myVariable    coco   window myVariable     riko    alert coco      display   riko   So  the value  coco  of myVariable becomes a variable coco   Because all the variables in the global scope are properties of the Window object

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use Object is great too   var a 123 var b 234 var temp     a  a  b  b  console log temp  a   temp  b

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eval   did not work in my tests  But adding new JavaScript code to the DOM tree is possible  So here is a function that adds a new variable   function createVariable varName varContent      var scriptStr    var   varName        varContent         var node scriptCode   document createTextNode  scriptStr     var node script   document createElement  script      node script type    text javascript    node script appendChild node scriptCode      var node head   document getElementsByTagName  head   0    node head appendChild node script      createVariable  dynamicVar    some content   console log dynamicVar

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Since ECMA- Javascript is all about Objects and Contexts  which  are also somekind of Object   every variable is stored in a such called Variable-  or in case of a Function  Activation Object    So if you create variables like this   var a   1      b   2      c   3    In the Global scope    NO function context   you implicitly write those variables into the Global object    window in a browser    Those can get accessed by using the  dot  or  bracket  notation   var name   window a    or  var name   window  a      This only works for the global object in this particular instance  because the Variable Object of the Global Object is the window object itself  Within the Context of a function  you don t have direct access to the Activation Object  For instance   function foobar        this a   1     this b   2      var name   window  a           undefined    alert name      name   this  a           1    alert name      new foobar      new creates a new instance of a self-defined object  context   Without new the scope of the function would be also global   window   This example would alert undefined and 1 respectively  If we would replace this a   1  this b   2 with   var a   1      b   2    Both alert outputs would be undefined  In that scenario  the variables a and b would get stored in the Activation Object from foobar  which we cannot access  of course we could access those directly by calling a and b

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Although this have an accepted answer I would like to add an observation    In ES6 using let doesn t work    x000D   x000D    this is NOT working   x000D  let t    skyBlue   x000D      m    gold   x000D      b    tomato   x000D   x000D  let color   window  b    x000D  console log color   x000D   x000D   x000D    However using var works   x000D   x000D    this IS working   x000D  var t    skyBlue   x000D      m    gold   x000D      b    tomato   x000D   x000D  let color   window  b    x000D  console log color   x000D   x000D   x000D    I hope this may be useful to some

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Just don t know what a bad answer gets so many votes  It s quite easy answer but you make it complex      If you want to get article count    var article count   1000  var type    article   this type   count     1000      in a function we use  this   alert article count

[javascript] Use dynamic variable names in JavaScript

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