Skip arguments in a JavaScript function - Stack Overflow

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I have a function like this:

function foo(a, b, c, d, e, f) {
}

In order to call this function only with an f argument, I know I should do:

foo(undefined, undefined, undefined, undefined, undefined, theFValue);

Is there a less verbose way to do this?

I have a function like this:

function foo(a, b, c, d, e, f) {
}

In order to call this function only with an f argument, I know I should do:

foo(undefined, undefined, undefined, undefined, undefined, theFValue);

Is there a less verbose way to do this?

• javascript

Share Improve this question Follow edited Apr 23, 2023 at 8:13 jonrsharpe 122k3030 gold badges264264 silver badges472472 bronze badges asked Sep 11, 2015 at 8:08 sergeserge 15.1k4141 gold badges140140 silver badges228228 bronze badges 5

• 1 Is the function written by you? Can you change it? – JJJ Commented Sep 11, 2015 at 8:10
• 3 You could use a single custom object as parameter instead a list of different parameters. – Davide Pastore Commented Sep 11, 2015 at 8:11
• @Juhana Yes, is my own function – serge Commented Sep 11, 2015 at 8:46
• FWIW, The var _ = undefined; foo(_,_,_,_,_, theFValue); solution is buried in this long answer. You would of course do the initial declaration of _ once, in some common utility file that you include in every js file. – ToolmakerSteve Commented Oct 27, 2020 at 0:30
• I could have sworn you could just do foo( , , , , , fValue); but I see that it is not possible. – Brain2000 Commented Jun 29, 2022 at 18:21

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9 Answers 9

Sorted by: Reset to default 84

Such:

foo(undefined, undefined, undefined, undefined, undefined, arg1, arg2);

.is equal to:

foo(...Array(5), arg1, arg2);

.or:

foo(...[,,,,,], arg1, arg2);

---

Such:

foo(undefined, arg1, arg2);

.is equal to:

foo(...Array(1), arg1, arg2);

.or:

foo(...[,], arg1, arg2);

---

Such:

foo(arg1, arg2);

.is equal to:

foo(...Array(0), arg1, arg2);

.or:

foo(...[], arg1, arg2);

You could use apply:

foo.apply(this, Array(5).concat([theFValue]));

In this case, 5 is the amount of parameters you want to skip.

Wrap that in a function:

function call(fn, skipParams, parameter) {
    fn.apply(this, Array(skipParams).concat([parameter]));
}

call(foo, 5, theFValue);

However, in that case the scope of this is different, so you may need to pass that, too:

function call(fn, skipParams, parameter, thisArg) {
    fn.apply(thisArg, Array(skipParams).concat([parameter]));
}

call(foo, 5, theFValue, this);

Then again, this implementation only allows 1 parameter to be passed. Let's improve that:

function call(fn, skipParams, parameters, thisArg) {
    fn.apply(thisArg, Array(skipParams).concat(parameters));
}

call(foo, 5, [theFValue, theGValue, theHValue], this);

That's starting to get a "little" verbose. It also doesn't handle missing parameters after the first parameter that well, unless you want to pass undefined:

call(foo, 5, [theFValue, theGValue, theHValue, undefined, theJValue], this);

---

Or, something completely different:

var _ = undefined;
foo(_,_,_,_,_, theFValue);

---

On a more serious note:

Your best option to deal with optional parameters, is to change the way you're handling parameters. Simply pass an object:

function foo(parameters){
    // do stuff with `parameters.a`, `parameters.b`, etc.
}

foo({c: 1, g: false});

This approach doesn't suffer from any of the drawbacks in the earlier examples.

A better way to deal with optional arguments is to pass an object whose attributes you look up:

function foo(options) {
    var a = options.a,
        b = options.b,
        c = options.c,
        d = options.d,
        e = options.e,
        f = options.f;
}

foo({ f: 15 });

Skip function:

const skip = (num) => new Array(num);

Skipping beginning params:

foo(...skip(4), f);

Skipping end params:

foo(f, ...skip(4));

Skipping middle params:

foo(f, ...skip(4), f2);

If you will pass an object with a property name f so you can use destructuring assignment with ES6 syntax like this:

function foo({ f }) {
  console.log(f);
}
    
foo({ g: 5, f: 10 });

I provide some methods that may help you achieve, as below,

1. Destructuring assignment (recommend)
2. Optional_chaining

---

Method1: Destructuring assignment

Example1

function Person(name, {id="007", age=-1, info={msg:null, mood:undefined}}) {
  return [name, id, age, info.msg, info.mood]
}

// 

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