Calling javascript function with 'arguments' using received 'arguments' issue

Question

My issue is best illustrated with a small code example available on JsFiddle:

function a() {
    alert("a: " + arguments.length);
    b(arguments);
}

function b() {
    alert("b: " + arguments.length);
}

a(33,445,67);

I have a function a called with a variable number of arguments, and I would like to call b with these arguments. Unfortunately, when I run the code above, it displays respectively 3 and 1, rather than 3 and 3.

How can I call b with all the arguments received in a?

You already call b with all the arguments, but like adeneo said, you call it with the argument-Object [33,445,67], this means your argument-Object in b looks like this [[33,445,67]]. — John Smith
– John Smith, Commented Mar 27, 2014 at 10:00

adeneo · Accepted Answer · 2014-03-27 10:13:04Z

6

arguments is an array-like object corresponding to the arguments passed to a function, so when b() is called there is only one argument, the array.
You can use apply(), which accepts the arguments as an array instead

function a() {
    alert("a: " + arguments.length);
    b.apply(undefined, arguments);
}

function b() {
    alert("b: " + arguments.length);
}

a(33,445,67);

FIDDLE

edited Mar 27, 2014 at 10:13

answered Mar 27, 2014 at 9:53

adeneo

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8 Comments

Arbel Over a year ago

Actually b.apply(null, arguments); or a relevant first argument will return the desired result.

adeneo Over a year ago

@Arbel - Why would null be more relevant than this when both functions are in the same parent scope ?

T.J. Crowder Over a year ago

@adeneo: "Why would null be more relevant than this when both functions are in the same parent scope ?" Scope and this have almost nothing to do with one another, in JavaScript. this is (until ES6's arrow functions) set primarily by how a function is called, not where it's defined.

adeneo Over a year ago

@T.J.Crowder - That's true, but in this case the functions are both defined in the same scope, and a() is called from that scope, so this would have the correct value, but as it's not used anyway it doesn't really matter.

T.J. Crowder Over a year ago

@adeneo: Right. But again, I would really stay away from combining "scope" and "this" when talking about JavaScript, as they really are unrelated, and the fact they're unrelated but people tend to think they're related is one of the biggest problems people have with JS.

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