Introducing Javascript's trim, trimLeft, and trimRight methods and default parameter values.


Javascript is a language which you either love or hate. But no matter how you feel the web has grown into the world's plaform which has made javascript an undeniable force to be reckoned with.

One positive side of javascript is that the standard library is lightweight which makes the language's API pretty easy to pick up. This is true but it has the unfortunate side effect of leaving javascript without some pretty basic functionality.

Fortunately the web is moving quickly and the multitude of preprocessors (coffeescript), supersets (typescript), and subsets (asm.js) as well as having javascript now on the server with node.js has brought to light the sore spots of javascript and has begun to show a clear path forward.

Check out altjs for a list of literally dozens of projects related to the future of Javascript.

But why?

The functionality we're about to discuss seems pretty basic. Thankfully our kids will grow up in a world where javascript supports this stuff. :p

All joking aside why does this matter? Can't we keep Javascript's standard library lightweight and have 3rd party libraries polyfill this stuff?

Of course we could do that but at this point it's clear that the web is the biggest development plaform of all time. The browser is the largest and most forgiving of run times which means we can count on an ocean of developers coming to this platform.

We can't count on all those developers learning about the correct libraries to get this functionality. We can't count on the 3rd party library creators standardizing on these features. And having native function calls tends to be more performant than calling 3rd party libraries.

I would expect the Javascript Standard Library to get larger going forward. Now on to the code!

trim, trimLeft, and trimRight

Introduced in Javascript 1.8.1

trim(), trimLeft, and trimRight method supported in Firefox 19+, Chrome 24+, Safari 6.0.2

console.log('   StringOne   '.trim() + 'StringTwo');
console.log('StringOne' + '   StringTwo'.trimLeft());
console.log('StringOne   '.trimRight() + 'StringTwo');
// all of the above statements log 'StringOneStringTwo'


Yea trimming. Like I said—we're talking about some pretty basic stuff here.

The trimLeft and trimRight methods both say Non-standard in their docs as well as ECMAScript Edition None.

Their sibling trim says Introduced in JavaScript 1.8.1 in it's docs as well as ECMAScript Edition ECMAScript 5th Edition.

I'm not entirely sure the status of trimleft and trimRight with regards to standards bodies and such but they appear to be implemented in the 3 desktop browsers which I tested.

Potential improvement

This could be improved by taking a second argument which is a list/range of characters to trim similar to PHP's trim implementation.

Default parameter values

Supported in Firefox 15+.

function foobar(buz = 'baz'){
 // logs 'baz'


This is far superior in readability to the current hack:

function foobar(buz){
  buz = buz || 'baz';
  // logs 'baz'

Potential improvement

Perhaps with a little added syntax we could have the default parameter value assigned to this. Ex:

function foobar(buz => 'baz'){
 // logs 'baz'


trim, trimLeft, and trimRight as well as default parameter values are some small additions which flesh out Javascript's API in places where it's badly needed. I expect a lot more of this kind of thing going forward.

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20 February 2013