How can I use Javascript functions as parameters for another function?

Question

Whenever I try to run this function in Chromium, I get the error message "Uncaught TypeError: Illegal invocation". Why does this occur, and how can I resolve it?

getOutput([alert], ["Hi!", "Hello!", "Lolwut?"]); //why doesn't this call "alert"
//for each of the arguments?

//this function is supposed to return the output of each function for each argument.
function getOutput(functions, arguments){
    for(var i = 0; i < functions.length; i++){
        for(var j = 0; j < arguments.length; j++){
            functions[i](arguments[j]); //why doesn't this call the function
        }
    }    
}

I believe this previous SO answer handles your case. Basically it comes back to scope. — Jacques Chester
– Jacques Chester, Commented Dec 18, 2012 at 3:50
@JacquesChester It appears to be addressing a slightly different problem - I'm specifically trying to call a function from a specific index of an array. — Anderson Green
– Anderson Green, Commented Dec 18, 2012 at 4:04
I think the biggest issue is that you're trying to call a native function from the specific index of an array. The invocation getOutput([function(msg){alert(msg);}], ["Hi!", "Hello!", "Lolwut?"]) works. — JayC
– JayC, Commented Dec 18, 2012 at 4:09
@AndersonGreen If you look at the accepted answer, it's the same basic logic as what I linked to. I'm happy to give matehat the credit on this one, he bothered to actually write an answer :D — Jacques Chester
– Jacques Chester, Commented Dec 18, 2012 at 4:23

matehat · Accepted Answer · 2012-12-18 04:32:43Z

3

EDIT:

Though the fix given here works, the reason seems to be as rbtLong suggested, that the native function (specifically here alert) is called outside of its context. Using a wrapper like this :

function F(arg) {alert(arg);}

in place of alert in your code as is makes the code run. Still, the suggested fix below works if you want to have a general purpose function that can take native function.

(BTW: The same occurs in Safari and Firefox)

It seems to have something to do with the array access construct not allowing invocation right after it. Maybe much like you can't do 1.toString(). You could quickly fix it like this :

getOutput([alert], ["Hi!", "Hello!", "Lolwut?"]);

function getOutput(functions, arguments){
    for(var i = 0; i < functions.length; i++){
        for(var j = 0; j < arguments.length; j++){
            var f = functions[i];
            f(arguments[j]);
        }
    }    
}

edited Dec 18, 2012 at 4:32

answered Dec 18, 2012 at 3:50

matehat

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4 Comments

JCOC611 Over a year ago

Placing a parenthesis around it might work too (functions[i])(arguments[i]);

matehat Over a year ago

I just tried and unfortunately it doesn't (that's what I was going to post first). ([alert][0])("hello!"); raises the same error.

JCOC611 Over a year ago

Maybe ([alert][0]).call(null, arguments[j])? (just for the sake of trying alternatives haha)

matehat Over a year ago

It does! But I guess the property access construct pretty much had to work. Otherwise it'd be breaking quite a lot of sites :)

Sudhir Bastakoti · Accepted Answer · 2012-12-18 03:59:57Z

1

do you mean something like:

function getOutput(fn, args) { 
 for(var f = 0; f < fn.length; f++){
    for(var j = 0; j < args.length; j++){
        fun = fn[f];
        fun.call(this, args[j]);
    }
  }

}
getOutput([alert], ["Hi!", "Hello!", "Lolwut?"]);

answered Dec 18, 2012 at 3:59

Sudhir Bastakoti

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Comments

rbtLong · Accepted Answer · 2012-12-18 04:01:40Z

1

i believe it is because you're calling an object outside of its context the method.call(args) described here http://www.devguru.com/technologies/ecmascript/quickref/call.html should allow for it.

functions[i].call(this, arguments[j])

edited Dec 18, 2012 at 4:01

answered Dec 18, 2012 at 3:55

rbtLong

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Comments

Algo · Accepted Answer · 2012-12-18 03:52:21Z

0

i belive it would be like this:

fun1(fun2('lol'));

or the hard way

var hi7 = fun2('lol')

fun1(hi7)

answered Dec 18, 2012 at 3:52

Algo

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4 Comments

Anderson Green Over a year ago

I don't see how this is relevant - can you explain further?

Algo Over a year ago

The question is asking how to use the output of a function of in a functions parameters

Greg Sansom Over a year ago

No, the question is asking about using pointers to the actual functions as parameters.

Algo Over a year ago

Oh sorry, very little JS Knowledge.

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