What is the most efficient way to empty a plain object in javascript?

Question

As stated Here, It seems that the most efficient way to empty an existing array (and NOT to allocate a new one) in javascript is to use:

array.length = 0;

Does the same operation work for plain objects? (aka "associative arrays" or "dictionaries") If not, what is the most efficient way to empty an existing javascript object?

I think that allocating a new one is not the best option, since it will push some extra work to the garbage collector, and will allocate some new memory on the heap, but I might be wrong.

I need a solution that works at least with Chrome and Firefox.

Solution

The shortest way to do that is to create a new object. You'd end up garbage collecting all the properties anyway.

var foo = {
    a: 5,
    b: 4
};
foo = {};

You could also iterate over the properties and remove them individually:

for (var prop in foo) {
    if (foo.hasOwnProperty(prop)) {
        delete foo[prop];
    }
}

It's also worth pointing out, as a matter of verbiage, that JavaScript has objects with properties, not associative arrays.

Comments

[Ignitor]

It should be noted that foo = {} creates a new object and leaves the original object as is. This makes a difference when there are other references to the original object: var foo = {a:5,b:4}; var bar = foo; foo = {}; At the end, baris still {a:5,b4} and not {} as one might expect.

[Dario]

@Ignitor How avoid that and propagate the change to bar too?

[Ignitor]

@Dario I guess you have to remove the properties individually using delete as stated in the answer.

[Dario]

Yes i do that with a for that cycle all elements and delete it