How Do I Traverse A Javascript Object And Check For Nulls?

Let's say I have a JavaScript object like: var obj = {}; obj.computers = {}; obj.computers.favorite = 'Commodore 64'; obj.computers.popular = 'Apple'; Now, I can easily check for

Solution 1:

You can really write:

(obj && obj.computers && obj.computers.favorite) || 'Unknown'

Solution 2:

You can do it with a helper function. If I understand your problem correctly, your objects may have arbitrary deep objects, and you want to access these arbitrary nested properties without cluttering your code. I built a Nested function which lets you get() arbitrary properties if they are set, or a default if they are not.

varNested = function() {};
// prop is a dot-separated path like "foo.bar.baz"Nested.prototype.get = function(prop, _default) {
    var current = this;
    $.each(prop.split("."), function(i, e) {
        current = current[e] || undefined;
        if (current == undefined)
            returnfalse;
    });
    return current || _default;
}

You can then write code like this

var fav = obj.get("computers.favourite", "Linux");
// this emulatesvar fav = obj.computers.favourite || "Linux"; // throws error

As you can see, it's not so much more typing. Sure, it doesn't feel like regular Javascript... Here is the fiddle.

Solution 3:

I wrote this to help you deal with one of your questions: "I need to see if obj.computers.favorite has been set".

Object.prototype.isset = function (/* string */ full_path)
{
    var props = full_path.split('.');
    varself = this; /* note that self is usually the window object */for (var ii = 0; ii < props.length; ++ii)
    {
        var prop = props[ii];
        var hasMoreComing = ii < props.length - 1 ? true : false;

        if (self[prop] !== null && typeof self[prop] === 'object' && hasMoreComing)
        {
            self = self[prop];
            continue;   // Move up one level.
        }
        elseif (hasMoreComing)
            returnfalse;    // ..because user queries a subproperty of a value typereturnself.hasOwnProperty(prop);
    }
};

Test-code:

var test = {};

test.kuk = {};
console.log( test.isset('kuk') );  // Prints true.

test.kuk.fitta = {};
console.log( test.isset('kuk.fitta') ); // Prints true.

test.kuk.fitta = null;
console.log( test.isset('kuk.fitta') ); // Prints true.

test.kuk.fitta = undefined;
console.log( test.isset('kuk.fitta') );  // Prints truedelete test.kuk.fitta;
console.log( test.isset('kuk.fitta') );  // Prints false

test.kuk.fitta = 123;
console.log( test.isset('kuk.fitta.doesnt.exist') );  // Prints false

Solution 4:

Unfortunately, there's not a super easy way to get around this, but you don't need to check for both null and undefined. Because null and undefined are both falsey, you can just do:

if (obj && obj.computers) {
  var fav = obj.computers.favorite || 'unknown';
}

It doesn't actually get around what your complaint is, but it's less painful than what you'd think.

Solution 5:

following function will take string as parameter and return object if exist

functiongetValueOrDefault(str , obj, deflt){
    var a = str.split("."); o = obj;
    for(var i =0; i < a.length; i++){
         o = obj[a[i]];
         if(!o){
           return deflt;
         }
    }
      return o;
}

var obj = {};
obj.computers = {};
obj.computers.favorite = "Commodore 64";
obj.computers.popular = "Apple";
getValueOrDefault('computers.favorite', obj, 'Unknown');

Note: You must not use var while assigning properties to object eg. var obj.computers.favorite is SYNTAX error.