naming redundancy in javascript function parameters

Question

How do I set default value of timing param?

function active_timer(timing){
    interval = setInterval(function(){
        console.log('interval');
    }, timing);
}

I can do like this

function active_timer(timing){
    var time = 1000;
    if(timing){
        time = timing
    }
    interval = setInterval(function(){
        console.log('interval');
    }, time);
}

My problem is with the naming, timing and time actually are the same thing, how can I write less redundant code in javascript?

interval = setInterval(function() { ... }, timing || 1000); — Niet the Dark Absol
– Niet the Dark Absol, Commented Aug 20, 2016 at 16:03

Niet the Dark Absol · Accepted Answer · 2016-08-20 16:03:54Z

1

An argument is a (local) variable just like any other.

timing = timing || 1000;

You can overwrite it without a care in the world.

answered Aug 20, 2016 at 16:03

Niet the Dark Absol

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1 Comment

Maria Jane Over a year ago

why not a var in front?

Script47 · Accepted Answer · 2016-08-20 16:07:57Z

1

You could add a check in your function,

if (typeof timing == 'undefined')
    timing = defaultValue;

or (ternary operator)

timing = (typeof timing == 'undefined') ? defaultValue : timing;

or

timing = timing || defaultValue

Example typeof

function x(y) 
{
  if (typeof y == 'undefined')
    y = 5;

  return y;
}

alert(x()); // 5

alert(x(25)); // 25

JSFiddle

Reading Material

typeof

MDN - Default Parameters

edited Aug 20, 2016 at 16:07

answered Aug 20, 2016 at 16:02

Script47

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Comments

T.J. Crowder · Accepted Answer · 2016-08-20 16:15:30Z

1

In ES2015 (aka "ES6") and later, you can specify a default value for the argument:

// ES2015+
function active_timer(timing = 1000) {
// -------------------------^^^^^^^
    interval = setInterval(function(){
        console.log('interval');
    }, timing);
}

In ES5 and earlier (well, technically all of this applies to ES2015+ as well): You can assign values to function arguments, so you don't need a separate variable unless you want one. If active_timer is called without any arguments, timing will have the value undefined.

You have a few options for how to determine you need to apply the default:

if (timing === undefined) {
    timing = 1000;
}

or

if (typeof timing === "undefined") {
    timing = 1000;
}

or

if (arguments.length === 0) {   // NOT RECOMMENDED
    timing = 1000;
}

(Not recommended because using arguments within a function can impact its performance.)

Or if you know active_timer will never be called with 0, you can use the curiously-powerful || operator:

function active_timer(timing){
    interval = setInterval(function(){
        console.log('interval');
    }, timing || 1000); // Only if you know timing won't be 0
}

The result of a || b is the value of a if it' truthy, or the value of b if a is falsy. The falsy values are 0, "", undefined, null, NaN, and of course, false.

edited Aug 20, 2016 at 16:15

answered Aug 20, 2016 at 16:10

T.J. Crowder

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6 Comments

Script47 Over a year ago

Ah, that last one is much better, didn't know it was possible (+1).

T.J. Crowder Over a year ago

@Script47: Apologies, I just moved it so it's not the last one anymore. :-) Yup, great new feature as of ES2015.

Script47 Over a year ago

How supported is ES6?

T.J. Crowder Over a year ago

@Script47: In modern browsers, support is quite good these days (kangax.github.io/compat-table/es6). But because there are still people using obsolete browsers, most of us transpile ES2015 to ES5 using tools like Babel.

Script47 Over a year ago

I found the ES6 string.includes function yesterday (slightly confused, thought it would be called contains...) and found it is supported in Chrome though not recognized in Webstorm(?), I may need to update it.

|

Michael Andorfer · Accepted Answer · 2016-08-20 16:46:13Z

0

You could use the default parameter and arrow function of ES2015:

function activeTimer(timing = 1000) {
    setInterval( () => {
        console.log('interval:' + timing);
    }, timing);
}

activeTimer();

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