Closures with arguments array of function

Question

Taking a look at code from Leaflet API

Getting lost with arguments and closures.

My second log output of arguments is an empty array. Shouldn't be the same at the first log.

limitExecByInterval: function (fn, time, context) {
    var lock, execOnUnlock;

    // Log output 1
    console.log(arguments);//[foo(), 10000, Window a.html]

    return function wrapperFn() {
        var args = arguments;

        if (lock) {
            execOnUnlock = true;
            return;
        }

        lock = true;

        setTimeout(function () {
            lock = false;

            if (execOnUnlock) {
                wrapperFn.apply(context, args);
                execOnUnlock = false;
            }
        }, time);

        //Log output 2
        console.log(args) //[]

        fn.apply(context, args);
    };
},

Arguments are different for the two functions..Thus different console log output. — Rakesh_Kumar
– Rakesh_Kumar, Commented Jan 7, 2015 at 8:42

Felix Kling · Accepted Answer · 2015-01-07 08:38:14Z

1

Shouldn't be the same at the first log.

No. Each function has its own arguments object. The second console.log call will log the arguments passed to wrapperFn, which doesn't seem to receive any in your test.

answered Jan 7, 2015 at 8:38

Felix Kling

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Comments

DhruvPathak · Accepted Answer · 2015-01-07 08:41:50Z

This is because arguments is a keyword inside a function , and does not behave like normal variables.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/arguments

You would need to store arguments in another variable to get the desired behavior

limitExecByInterval: function (fn, time, context) {
        var lock, execOnUnlock;

        // Log output 1
        console.log(arguments);//[foo(), 10000, Window a.html]
        var myArgs = arguments ;

        return function wrapperFn() {
            var args = myArgs;  /* not using the keyword 'arguments' here */

            if (lock) {
                execOnUnlock = true;
                return;
            }

            lock = true;

            setTimeout(function () {
                lock = false;

                if (execOnUnlock) {
                    wrapperFn.apply(context, args);
                    execOnUnlock = false;
                }
            }, time);

            //Log output 2
            console.log(args) //[]  This will print an array now.

            fn.apply(context, args);
        };
    },

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