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

You won't be able to do this without some sort of function, as JavaScript doesn't have a generic getter/setter method for objects (Python, for example, has __getattr__). Here's one way to do it:

function add_property(object, key, value) {
    var keys = key.split('.');

    while (keys.length > 1) {
        var k = keys.shift();

        if (!object.hasOwnProperty(k)) {
            object[k] = {};
        }

        object = object[k];
    }

    object[keys[0]] = value;
}

If you really want to, you could add it to the prototype of Object. You can call it like so:

> var o = {}
> add_property(o, 'foo.bar.baz', 12)
> o.foo.bar.baz
12

Answer 2

I've come up with something, really custom as well, but it works as far as I have tested.

function dotted_put_var(str,val) {
    var oper=str.split('.');
    var p=window;
    for (var i=0;i<oper.length-1;i++) {
        var x=oper[i];
        p[x]=p[x]||{};
        p=p[x];
    }
    p[oper.pop()]=val;
}

Then, a complex variable can be set like this, ensuring that every links will be created if not already:

dotter_put_var('test.hello.world', 'testvalue'); // test.hello.world="testvalue";

See this working FIDDLE.

Answer 3

let test = {};
test = {...test, hello: {...test.hello, world: 'Hello does exist!'}};
console.log(test);

When using the spread operator, the value can be undefined, it'll automatically create an object.

Answer 4

This will add a property hello whose value is {world: 'Hello world!'} to the test object, if it doesn't exist. If you have a lot of these objects, you can just iterate over them and apply this function. Note: uses lodash.js

var test = {};
_.defaults(test, { hello: {world: 'Hello world!'} });    

Which is actually a convenience method for saying:

var defaults = _.partialRight(_.assign, function(a, b) {
  return typeof a == 'undefined' ? b : a;
});        
defaults(test, { hello: {world: 'Hello world!'} });

Note: _.defaults uses loops to achieve the same thing as the second block.

P.S. Checkout https://stackoverflow.com/a/17197858/1218080

Answer 5

I use this:

Object.prototype.initProperty = function(name, defaultValue) {
  if (!(name in this)) this[name] = defaultValue;
};

You can later do f.e.:

var x = {a: 1};
x.initProperty("a", 2); // will not change property a
x.initProperty("b", 3); // will define property b
console.log(x); // => {a: 1, b: 3}

Answer 6

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.