How to create an object property from a variable value in JavaScript

Question

I want to add a new property to  myObj   name it  string1  and give it a value of  string2   but when I do it it returns  undefined   var myObj   new Object  var a    string1   var b    string2   myObj a   b   alert myObj string1     Returns  undefined  alert myObj a     Returns  string2    In other words  How do I create an object property and give it the name stored in the variable  but not the name of the variable itself

User · Answer

ES6 introduces computed property names  which allow you to do  var myObj     a   b     Note browser support is currently negligible

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Ecu  if you do myObj a  then it looks for the property named a of myObj  If you do myObj a   b then it looks for the a valueOf   property of myObj

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Oneliner   obj    function attr  val   var a       a attr  val  return a      hash   5     Or   attr    hash   val   5  var obj    obj     obj attr  val  obj     Anything shorter

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There s the dot notation and the bracket notation  myObj a    b

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As  scope is an object  you can try with JavaScript by    scope  something      hey    It is equal to    scope something    hey    I created a fiddle to test

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The following demonstrates an alternative approach for returning a key pair object using the form of  a  b   The first example uses the string  key  as the property name  and  val  as the value  Example  1   function o a b  return o a  b o       key   val     Example   2  var obj     foo   bar      function o a b  return o a  b o   obj  key   val     As shown in the second example  this can modify existing objects  too  if property is already defined in the object  value will be overwritten    Result  1    key   val    Result  2    foo   bar   key   val

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You could just use this   function createObject propName  propValue       this propName    propValue    var myObj1   new createObject  string1   string2      Anything you pass as the first parameter will be the property name  and the second parameter is the property value

User · Answer

You cannot use a variable to access a property via dot notation  instead use the array notation   var obj          name     jroi     var a    name   alert obj a     will not work alert obj a      should work and alert jroi

User · Answer

Dot notation and the properties are equivalent  So you would accomplish like so   var myObj   new Object  var a    string1   myObj a     whatever   alert myObj string1     alerts  whatever

[javascript] How to create an object property from a variable value in JavaScript?

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