Last Updated: July 26, 2016
· joseym

JavaScript: Assign value to object from string

Introduction and disclaimer

Some time back I found myself in need of a way to take a string from dot notation and build/update an object from that.

I scoured the internet and found several methods, none of which quite did what I needed them to do; some would only update an existing object, while others would only create a new object. Most only worked down to a handful of levels.

I took what I found and used them as a reference to create this handy method. Very little of this method is purely my brainchild, but rather a combination of help from the geniuses that troll StackOverflow.

I also want to admit that there are likely other ways to go about this exact same thing, some may even be more elegant.

String toObject

String.prototype.toObject = function( obj, value ) {
  var names = this.split('.');
  // If a value is given, remove the last name and keep it for later:
  var lastName = arguments.length === 2 ? names.pop() : false;
  // Walk the hierarchy, creating new objects where needed.
  // If the lastName was removed, then the last object is not set yet:
  for( var i = 0; i < names.length; i++ ) {
    obj = obj[ names[i] ] = obj[ names[i] ] || {};
  // If a value was given, set it to the last name:
  if( lastName ) obj = obj[ lastName ] = value;
  // Return the last object in the hierarchy:
  return obj;


Using the method is simple. As its an extension of the javascript String object you mere chain it from the dot notated sting, like so:

var newObject = {};
''.toObject(newObject, 'Josey');

Which, if you then log newObject you will get the following:

  contact: {
    name: {
      first: 'Josey'


I hope this ends up helping someone else; I've found it immensely useful for things like shortcuts to update data via url query strings.

3 Responses
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I know of a couple different ways for this to be useful in some of my projects. Especially working with things like properties files that have a syntax similar to my.little.object=foobar per line. A couple of tweaks, and this could become very, very useful for that!

I wrote something similar to this for a project just recently. Except instead of creating an object, I'm searching for it within a context. In other words, "Ns.Utilities.MyUtility" would search for "Ns" inside "window" (unless another context was given), "Utilities" inside that result, and finally "MyUtility" inside that result. I have found it very, very useful. I'll see if I can carve out the time to throw it into a tip!

over 1 year ago ·

I would be very interested indeed to see your implementation.

Does it create the object if it doesn't exist in the context?

over 1 year ago ·

I totally forgot to get back on here after your reply!

But check out my implementation here.

Most specifically:

var my = { little: { object: "foobar" } };

function getObjectFromString(objRef) {
    myObj = window;

    var refParts = objRef.split('.');
    for (var c=0;c<refParts.length;c++) {
        var classVar = refParts[c];
        if (!classVar || !myObj[classVar]) {
            myObj = null;

        myObj = myObj[classVar];

    return myObj;

var result = getObjectFromString("my.little.object");

console.log(result); // "foobar"

It's not the best implementation in the world, but I wanted to avoid function recursion, so I decided to use a for loop instead that simply sets a variable over and over again. This changes the context and allows you to traverse the dimensions of the object based on the string provided.

over 1 year ago ·