Named arguments in JavaScript

Question

Say I have a function like this

function myFunc(a, b, c)
{
    if(a!=undefined) this.a = a;
    if(b!=undefined) this.b = b;
    if(c!=undefined) this.c = c;
}

And I want to set only the value for b, then I could do something like this.

myFunc(undefined, "some Value for b", undefined);

But I was wondering if there was a way in which I could do something like this for setting the value of b

myFunc(b:"some value for b");

This is probably wrong, but you probably see what I mean. I want to specify the name of the property along with the value so that I do not have to worry about passing undefined values. How would I do this?

Also feel free to change the title, I have no idea what this question should be called.

This is a solution: ivanzuzak.info/2009/08/09/named-arguments-in-javascript.html — Populus
– Populus, Commented Mar 19, 2013 at 19:06
"I have no idea what this question should be called". Funniest stackoverflow moment of my life so far... — imulsion
– imulsion, Commented Mar 19, 2013 at 19:07
What's the intention with this.a etc? You're not instantiating an object, so this will be the global object. — bfavaretto
– bfavaretto, Commented Mar 19, 2013 at 19:09
@bfavaretto yes I am using this function for creating objects, even though not shown here — Joe Slater
– Joe Slater, Commented Mar 19, 2013 at 19:10
"Do you mean to say that the example I gave actually works?" Only if you change the syntax to use object literal notation (ie add {} around b:"some value". The key concept is that you're passing an Object as an argument. Objects can be created using the object literal notation, which looks like this: { propA: 'valueA', propB: 'valueB' } — jahroy
– jahroy, Commented Mar 19, 2013 at 19:20

Travis J · Accepted Answer · 2013-03-19 19:32:30Z

4

jsFiddle Demo

Sure, just use this:

function myFunc(options)
{
 if(typeof(options['a']) != "undefined") this.a = options['a'];
 if(typeof(options['b']) != "undefined") this.b = options['b'];
 if(typeof(options['c']) != "undefined") this.c = options['c'];
}

and then call it with

var func = new myFunc({b:"some value for b"});
console.log(func.b);//"some value for b"

edited Mar 19, 2013 at 19:32

answered Mar 19, 2013 at 19:07

Travis J

82.5k43 gold badges213 silver badges280 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

Travis J Over a year ago

@Ojay - You were correct, the options object needs to check for a string index and not a variable one.

Joe Slater Over a year ago

@TravisJ I probably think that he meant that you are missing brackets

Travis J Over a year ago

@AnkurSharma - Ah, the simple things. Fixed. ;)

Joe Slater Over a year ago

@OJay I am wondering why obj[i] works and why not obj.i. Look here -jsfiddle.net/GyBdz . Just trying to understand what is going on here.

OJay Over a year ago

@AnkurSharma in the case of the for in loop, you are assigning the property name of the passed in object to the variable i. this[i] works because it replaces the i with the current property (i.e. b), so actually assigned this.b, whereas this.i is not using the variable i, you are actually creating a property of i on the function. try it, instead of console.log(func.b) with the second one, change it to console.log(func.i)

|

OJay · Accepted Answer · 2013-03-19 19:55:30Z

1

yes, pass in an object literal

function myFunc(options)
{
    if(options.a!=undefined) this.a = options.a;
    if(options.b!=undefined) this.b = options.b;
    if(options.c!=undefined) this.c = options.c;
}

and call like this

var var1 = new myFunc({b:"some value for b"});

or for a more dynamic, extensible way ( as mentioned)

function myFunc(obj)
{
    for (var i in obj)
    {
        if(obj.hasOwnProperty(i))
        {
            this[i]=obj[i];
        }
    }
}

var func = new myFunc({b:"some value for b"});
console.log(func.b);//"some value for b"

edited Mar 19, 2013 at 19:55

answered Mar 19, 2013 at 19:08

OJay

4,9313 gold badges29 silver badges47 bronze badges

1 Comment

Travis J Over a year ago

note that if called like that, it will attach b to the window object.

jahroy · Accepted Answer · 2013-03-19 19:18:32Z

1

You can achieve this by passing an Ojbect as an argument:

var someObject = { a: 'some A value', b: 'some B value' };

myFunc(someObject);

This is a very common practice.

For example, jQuery uses this construct often.

If you look at the documentation for jQuery.animate(), you can see it accepts a Plain Object as the first argument.

edited Mar 19, 2013 at 19:18

answered Mar 19, 2013 at 19:10

jahroy

22.8k10 gold badges62 silver badges111 bronze badges

Collectives™ on Stack Overflow

Named arguments in JavaScript

3 Answers 3

8 Comments

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

8 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related