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Say I have a function that takes an arbitrary number of arguments (the last is callback):

xxx.create ('arg1', 'arg2', ..., 'arg10', callback) {
    ...
}

But it's ugly. I want to be able to extract the first few parameters and do something like:

var args = ['arg1', 'arg2', ..., 'arg10']
xxx.create (args.explode(), callback) {
    ...
}

Of course I can write a wrapper for xxx.create(), but I want it to be clean.

Thanks.

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2 Answers

up vote 1 down vote accepted

You're looking for Function.apply.

var args = ['arg1', 'arg2', ..., 'argN'];
xxx.create.apply(xxx, args.concat(callback)) {
    // ...
}

I used Array.concat so as to not mutate the original args array. If that's not a problem, either of these will suffice:

var args = ['arg1', 'arg2', ..., 'argN', callback];
xxx.create.apply(xxx, args) {
    // ...
}

// or

var args = ['arg1', 'arg2', ..., 'argN'];
args.push(callback);
xxx.create.apply(xxx, args) {
    // ...
}

Now, if you wanted to use a wrapper instead of exposing the Function.apply call:

function create_wrapper() {
    xxx.create(xxx, arguments);
}

// then

create_wrapper('arg1', 'arg2', ..., 'argN', callback);

will do the job.

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up vote 0 down vote

The local arguments variable can help here:

foo = function(){
  // convert local 'arguments' object to array ...
  argsArray = Array.prototype.slice.call(arguments);

  // pop the callback off
  callback = argsArray.pop();

  // the callback alerts the remaining, variable-length arguments list
  callback(argsArray);
};

here's the jsfiddle: http://jsfiddle.net/K38YR/

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