Automatically create object if undefined

Question

Is there an easy way to automatically add properties to objects if they don\'t allready exist?

Consider the following example:

var test = {}
test.hel         


        

Answer 1

I've made some changes on columbus's answer to allow create arrays:

function addProps(obj, arr, val) {

  if (typeof arr == 'string')
    arr = arr.split(".");

  var tmpObj, isArray = /^(.*)\[(\d+)\]$/.exec(arr[0])
  if (isArray && !Number.isNaN(isArray[2])) {
    obj[isArray[1]] = obj[isArray[1]] || [];
    obj[isArray[1]][isArray[2]] = obj[isArray[1]][isArray[2]] || {}
    tmpObj = obj[isArray[1]][isArray[2]];
  } else {
    obj[arr[0]] = obj[arr[0]] || {};
    tmpObj = obj[arr[0]];
  }

  if (arr.length > 1) {
    arr.shift();
    addProps(tmpObj, arr, val);
  } else
    obj[arr[0]] = val;

  return obj;

}


var myObj = {}
addProps(myObj, 'sub1[0].sub2.propA', 1)
addProps(myObj, 'sub1[1].sub2.propA', 2)

console.log(myObj)

I think that is possible to allow use "sub1[].sub2..." to just push into the sub1 array, instead of specify the index, but that's enough for me now.