javascript test for existence of nested object key

Question

If I a reference to an object -

var test = {};

that will potentially (but not immediately) have nested objects, something like -

{ level1:{level2:{level3:'level3'}} };

what is the best way to test for the existence of keys in the most deeply nested objects?

This -

alert(test.level1);

returns 'undefined', but this -

alert(test.level1.level2.level3);

fails.

I'm currently doing something like this -

if(test.level1 && test.level1.level2 && test.level1.level2.level3) {
    alert(test.level1.level2.level3);
}

but I was wondering if there's a better way.

Thanks much.

Answer 1

how about

try {
   alert(test.level1.level2.level3)
} catch(e) {
 ...whatever

}

Answer 2

You have to do it step by step if you don't want a TypeError, because if one of the members is null or undefined, and you try to access a member an exception will be thrown.

You can either simply catch the exception, or make a function to test the existence of multiple levels, something like this:

function checkNested(obj /*, level1, level2, ... levelN*/) {
  var args = Array.prototype.slice.call(arguments),
      obj = args.shift();

  for (var i = 0; i < args.length; i++) {
    if (!obj.hasOwnProperty(args[i])) {
      return false;
    }
    obj = obj[args[i]];
  }
  return true;
}

var test = {level1:{level2:{level3:'level3'}} };

checkNested(test, 'level1', 'level2', 'level3'); // true
checkNested(test, 'level1', 'level2', 'foo'); // false

Answer 3

You can easily read an object property at any depth, if you handle the name like a string- 't.level1.level2.level3'.

window.t={level1:{level2:{level3: 'level3'}}};

function deeptest(s){
    s= s.split('.')
    var obj= window[s.shift()];
    while(obj && s.length) obj= obj[s.shift()];
    return obj;
}

alert(deeptest('t.level1.level2.level3') || 'Undefined')

It returns undefined if any of the segments is undefined.

Answer 4

i usually just do something like:

if(typeof test.level1.level2.level3 != 'undefined') {
  alert('woo!');
}

Answer 5

I automated the process

if(isset(object,["prop1","prop2"])){
// YES!

}

function isset(object, props){
    var dump;
    try {
        for(var x in props){
            if(x == 0) {
                dump = object[props[x]];
                return;
            }
            dump = dump[props[x]];
        }
    } catch(e) {
        return false;
    }

    return true;
}

Answer 6

Here is a pattern I picked up from Oliver Steele:

var level3 = (((test || {}).level1 || {}).level2 || {}).level3;
alert( level3 );

In fact that whole article is a discussion of how you can do this in javascript. He settles on using the above syntax (which isn't that hard to read once you get used to it) as an idiom.