js build object path in property assignment

Question

is there a way to automatically create subobjects in an assignment after construction, i.e.

var obj = {};
obj.a.b.c=13;

the above gives me a "obj.a is undefined" error

i wrote a function to do this, but wondered if there was an easier way

_setObjectProperty(obj,13,['a','b','c']);
function _setObjectProperty(obj,value,loc)
{
    if(loc.length>1) {
        obj[loc[0]] = obj[loc[0]] || {};
        _setObjectProperty(obj[loc[0]],value,loc.splice(1));
    }
    else if(loc.length===1) {
        obj[loc[0]]=value;
    }
}

Cristian Sanchez · Accepted Answer · 2011-08-15 20:11:51Z

12

No, there's no built in way to do this in JavaScript. The only way is to create your own function like you did. If you want the convenience of the dot operator/notation you can use the following function:

var set = function(path, value, root) {
  var segments = path.split('.'),
      cursor = root || window,
      segment,
      i;

  for (i = 0; i < segments.length - 1; ++i) {
     segment = segments[i];
     cursor = cursor[segment] = cursor[segment] || {};
  }

  return cursor[segments[i]] = value;
};

set("a.b.c", 2);

console.log(a.b.c) // => 2

answered Aug 15, 2011 at 20:11

Cristian Sanchez

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2 Comments

Tristan Over a year ago

This is brilliant but how does it work exactly? I don't see where the root gets updated.

Diosney Over a year ago

It seems that the root is the object were you may want to attach that path to.

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