How safe is it to overload a javascript function?

Question

Let's say I have:

function myFunk(param1) {
    if (param1) {
            // do stuff
    } 
}

and I alter this to ...

function myFunk(param1, param2) {
    if (param2) {
            // do stuff
    }
}

param2 can only ever be true or false. Is this safe?

And what do you mean with "overload" ? You're changing the function, not overloading it. — Denys Séguret, Jun 26 '13 at 12:54
See [Function overloading in Javascript - Best practices](http://stackoverflow.com/questions/456177/function-overloading-in-javascript-best-practices) — PP., Jun 26 '13 at 12:54
Well that will work but its not overloading its replacing one function with another. — Mark Broadhurst, Jun 26 '13 at 12:54
Functions can't be overloaded in JavaScript because the arguments are typeless. Also, you may define a function with say 2 args, but you can pass more/less than 2 args and it won't fail. So what you are doing is replacing the same function with a new definition. — mohkhan, Jun 26 '13 at 12:55

score 2 · Accepted Answer · edited May 23 '17 at 12:05

function myFunk(param1, param2) {
    if (param2) {
            // do stuff
    }
}
param2 can only ever be true or false.

No. It can have any value. If the function is called with only one argument (myFunk("something")), then the param2 will have the value undefined. Which is falsy (like null, "", 0 or NaN) of course, so as expected your if-statement will not be executed.

Is this safe?

It's the standard way to have optional arguments in JavaScript, yes. For further details see Function overloading in Javascript - Best practices

score 0 · Answer 2 · answered Jun 26 '13 at 12:55

0

In this case, I feel it would be more clear if you use function variable approach.

var myFunk = function(param1) {
    if (param1) {
            // do stuff
    } 
}

and I alter this to ...

myFunk = function(param1, param2) {
    if (param2) {
            // do stuff
    }
}

It is now very clear what is happening, and the previous version of function myFunc does not exist anywhere.

edit more info

If you call function(param1, param2) {} with only one parameter, then typeof param2 == "undefined" will return true. For example:

myFunk = function(param1, param2) {
    if (typeof param2 == "undefined") {
        // do stuff with only param1
    }
}

answered Jun 26 '13 at 12:55

000

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you should use `param2 === undefined` rather than the string version of it. – Mark Broadhurst Jun 26 '13 at 13:01
No... `typeof` returns a string. This is safe for the case that `undefined` is redefined. – 000 Jun 26 '13 at 13:02
which is why i dropped the `typeof` from my code. – Mark Broadhurst Jun 26 '13 at 13:03
That's a terrible reason to drop it. Using typeof is the accepted way to test for define-ness – 000 Jun 26 '13 at 13:03
http://stackoverflow.com/questions/2703102/typeof-undefined-vs-null – 000 Jun 26 '13 at 13:04
I think he meant "altering the code" instead of "overwriting with a second definition" – Bergi Jun 26 '13 at 13:05
Who knows what OP meant. A question this vague deserves to be closed. – 000 Jun 26 '13 at 13:05
yes see `undefined` is maybe surprisingly always defined, and if you have misspell your parameter I would prefer an error rather than a silent failure. – Mark Broadhurst Jun 26 '13 at 13:08
I'm not following what you mean. – 000 Jun 26 '13 at 13:11
if you had `typeof para2 == "undefined"` will be always be false where as it should be an error since you have misspelt `param2`. `undefined` is global so always exists (although it can be redefined). – Mark Broadhurst Jun 26 '13 at 13:22
And that would be your own damn fault. Same thing would happen if you typo the variable name *anywhere* – 000 Jun 26 '13 at 13:24
+1, for the excellent explanation why overloading isn't possible – Pranav Singh Jun 26 '13 at 15:20

score 0 · Answer 3 · answered Jun 26 '13 at 12:58

You cannot overload functions in javascript. you would be better checking the arguments or checking for undefined in order to see what the caller is trying to do. for example

function myFunk(param1, param2) {
    if (param2) {
            // do stuff
    }
}

myFunk(1); // if does not execute

myFunk(1, 2); // if executes

however if you pass a falsy value for the second param then the if will still not execute

myFunk(1,0);  // if does not execute

score -1 · Answer 4 · answered Jun 26 '13 at 13:06

-1

Function overloading is not possible in javascript, if you made two same name function in same scope, always last function with that name will be called irrespective of number of parameters.

answered Jun 26 '13 at 13:06

Pranav Singh

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Downvote ??? any reasons... – Pranav Singh Jun 26 '13 at 13:08
I'd like to know as well, for my answer too. – 000 Jun 26 '13 at 13:09
Well if someone asks that is not feasible in a language, you can only say that's not possible. Any further explanation is waste of time to be specific – Pranav Singh Jun 26 '13 at 13:11
Yep I got randomly down-voted too. :-( – Mark Broadhurst Jul 12 '13 at 10:12

How safe is it to overload a javascript function?

4 Answers4