寻找一些js范围的黑客

Question

Here some interesting behaviour of javascript function arguments variable that you may be or maybe not aware of:

function foo(bar) {
    console.log('bar was:', bar); 
    arguments[0] = 'zap';        
    console.log('bar now:', bar); 
}  

foo('bam'); 
// bar was: bam
// bar now: zap

As you can see bar variable now pointing out to another value.

I want to make use of such behavior in a slightly strange way, I want to know is it possible to change argument value from the outside of the function scope somehow?

Maybe using call/apply, or some other trycky js features?

So I can change the value of function argument after it was called, for example:

function chooseNumber(number) { 
    setInterval(function() { 
        console.log('I choosed:', number) 
    }, 1000) 
}

chooseNumber(1);
// I choosed: 1
// I choosed: 1
// I choosed: 1
// ...

Then if I dicided to change my mind, how can I make so that initial function would output:

// I choosed: 2
// I choosed: 2
// I choosed: 2
// ...

Answer 1

No, it should not be possible especially not with EcmaScript 5 strict mode. However hackery can succeed in non-strict mode. The following tries to modify arguments within a closure via a stored arguments object; works on Firefox.

var argsave, bar;

(function foo(a) {
    argsave = arguments;
    bar = function () {
        alert("a is now: " + a);
    };
} (13));

bar(); // --> a is 13
argsave[0] = 42;
bar(); // --> a is 42

However you do not need it, and should not use it; if you want to modify a value within a closure, then use a function within the closure:

var setA, bar;

(function foo(a) {
    bar = function () {
        alert("a is now: " + a);
    };
    setA = function (newA) {
        a = newA;
    };
} (13));

bar(); // --> a is 13
setA(42);
bar(); // --> a is 42

Answer 2

A better way is to clear previous interval and then register your setInterval again with new behaviour as follows.

function chooseNumber(number) { 
    var int = setInterval(function() { 
        console.log('I choosed:', number) 
    }, 1000) ; 
    return int;
}

var interval = chooseNumber(10);

if(someCondition ){
    clearInterval(interval);
    interval = chooseNumber(20);

}