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javascriptmemory-leaksarguments
zangw
zangw

Reputation: 48406

JavaScript: arguments leak var array.slice.call?

In this post Optimization Killers, the following codes are mentioned to argument leak.

function leaksArguments2() {
    var args = [].slice.call(arguments);
}

However, I cannot understand that why arguments can leak through Array.slice?

Upvotes: 2

Views: 694

Answers (1)

Kevin Borders
Kevin Borders

Reputation: 2992

[].slice.call(arguments) "leaks" arguments because it retains a reference to the arguments object. Leaking the arguments object kills optimization because it forces V8 to instantiate the arguments as a Javascript object instead of optimizing them into stack variables.

You should just be able to create a copy of the arguments array in a way that doesn't retain an object reference as mentioned in the original post:

function doesntLeakArguments() {
                    //.length is just an integer, this doesn't leak
                    //the arguments object itself
    var args = new Array(arguments.length);
    for(var i = 0; i < args.length; ++i) {
                //i is always valid index in the arguments object
        args[i] = arguments[i];
    }
    return args;
}

Upvotes: 2

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