CODEWITHSUNDEEP
javascriptgarbage-collectionobject-pooling
FreddyNoNose
FreddyNoNose

Reputation: 548

Javascript GC apply existing object

Suppose we have a pool of objects (aka an array). Then we Constructor.apply(obj, arguments). 

    var obj = objectPool[nextAvailableIndex];
    obj.index = nextAvailableIndex;
    nextAvailableIndex += 1;
    Constructor.apply(obj, arguments);
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

What does this do to the existing Obj? Is the memory reused? Does this help avoid GC? Isn't it essentially the same as new or is it similar but different?

Upvotes: 0

Views: 80

Answers (2)

Bergi
Bergi

Reputation: 665130

What does this do to the existing Obj?

It calls the Constructor on it, with its this value set to the obj. What Constructor does exactly we do not know, but in general it is supposed to initialise a fresh instance.

Is the memory reused?

Depends in part on what Constructor does, and how it deals with non-fresh instances. But yes, obj was never released as it stayed in the objectPool array, and in contrast to new Constructor(…) no new object that inherits from Constructor.prototype is instantiated.

Upvotes: 0

rousan
rousan

Reputation: 381

Suppose we consider a code snippet like this: 

function Constructor() {
    this.prop = "some_value";
}
var objectPool = [{}, {}, {}];
var nextAvailableIndex = 0;
function Caller() {
    var obj = objectPool[nextAvailableIndex];
    obj.index = nextAvailableIndex;
    nextAvailableIndex += 1;
    Constructor.apply(obj, arguments)
}

In this case when the Caller is called then everytime a new local variable is created named 'obj', but after executing the Caller, that variable is freed.

That's it.

Upvotes: 1

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