How shall I delete objects in Javascript to properly destroy them (call destructors if there are any?) and prevent memory leaks? I've seen two ways:
delete obj;
and
obj = null;
But even after reading this I have not understood what is really the difference and what should I use.
Also, I guess there are not real destructors in Javascript, but in case of complex relationship of multiple objects is it really enough to rely on garbage collector to prevent memory leaks?
One major difference between the two is the value of obj after the operation. Consider
x = 42
x = null
console.log(x) // prints: null
delete x;
console.log(x) // prints: undefined
Assigning null is giving a new value to an existing property. It will still exist after the operation. When you delete a property it is removed entirely.
Google has something to say about delete:
Prefer this.foo = null
Foo.prototype.dispose = function() {
this.property_ = null;
};
Instead of:
Foo.prototype.dispose = function() {
delete this.property_;
};
In modern JavaScript engines, changing the number of properties on an object is much slower than reassigning the values. The
deletekeyword should be avoided except when it is necessary to remove a property from an object's iterated list of keys, or to change the result ofif (key in obj).
Edit
Some performance test: http://jsperf.com/delete-vs-nullify
The article you have linked says that delete only deletes a reference, therefore there is no difference between the two really performance wise. The only theoretical difference is the garbage collector will be more efficient because it's been explicitly told what to do, but unless you have incredibly large complex objects with many references in hard to reach locations it shouldn't be an issue.
The other answer on the question explains an actual usecase that highlights a difference, ie. removing a property from an object. Accessing it would then give you undefined rather than null.
Here's an example of the latter: http://jsfiddle.net/YPSqM/
function cat() { this.name = 'mittens'; };
var myCat = new cat();
alert(myCat.name); // 'mittens'
myCat.name = null;
alert(myCat.name === null); // 'true' as it is null but not undefined
delete myCat.name;
alert(myCat.name === undefined); // 'true' as it is undefined (but not null)
