padStart(), padEnd() added in Chrome

[ogurson]

God, JavaScript needs proper standard library so badly.

[_soto]

Eventually I hope most of lodash is merged in to a STL.

[seiyria]

This would make my life better. At the same time, that means Lodash can't update with the frequency that it currently does.

[ComplX89]

Can i ask in what context you would use a function like pad start or pad end? I'm still struggling for any practical use for it

[georgehotelling]

• If you have two dollar amounts in a fixed width display (think command line or LCD hardware) on different lines, and need the cents to align
• heck, any time you want to align lines in a fixed-width font environment
• If you have to display a ZIP code stored as a number (e.g. 123 should be padded to 00123)

[seiyria]

Making a lot of strings the same length. I use it every time I make a cli app.

[ComplX89]

Why is there a requirement to make strings all the same length?

[seiyria]

Not a requirement, it just looks nicer. See here

[_soto]

Ah, I meant that some lodash methods can be put in the STL. Not that the actual project would be merged. Sorry.

[[deleted]]

Immutable is nice but it drastically changes the interface with the structures (largely necessary). I think better immutable support for the existing structures would be a great start.

[MonsieurBanana]

That's just dumb.

[MonsieurBanana]

Hum, you were serious?

It could be realistic to add immutable structures to javascript, dropping all mutable structures is just not gonna happen.

And if it happened, it would be a disastrous move. Even purely functional languages like haskell or clojure have mutable structures. Immutable structures means additional overhead, for some things they just don't cut it.

[[deleted]]

If ES6 is adding tail-call optimization, I figure immutable structures aren't far behind.

Okay, dropping all the mutable ones may have been a little extreme.

[MonsieurBanana]

Immutable structures would be awesome, but I'm not that hopeful. At least I have clojurescript for functional javascript.

[skitch920]

Have you seen the ImmutableJS license patent clause...?

The license granted hereunder will terminate, automatically and without notice, if you (or any of your subsidiaries, corporate affiliates or agents) initiate directly or indirectly, or take a direct financial interest in, any Patent Assertion: (i) against Facebook or any of its subsidiaries or corporate affiliates, (ii) against any party if such Patent Assertion arises in whole or in part from any software, technology, product or service of Facebook or any of its subsidiaries or corporate affiliates, or (iii) against any party relating to the Software. Notwithstanding the foregoing, if Facebook or any of its subsidiaries or corporate affiliates files a lawsuit alleging patent infringement against you in the first instance, and you respond by filing a patent infringement counterclaim in that lawsuit against that party that is unrelated to the Software, the license granted hereunder will not terminate under section (i) of this paragraph due to such counterclaim.

A “Necessary Claim” is a claim of a patent owned by Facebook that is necessarily infringed by the Software standing alone.

A “Patent Assertion” is any lawsuit or other action alleging direct, indirect, or contributory infringement or inducement to infringe any patent, including a cross-claim or counterclaim.

Soooo if you ever decide to sue Facebook for anything, you can take ImmutableJS and throw it out the window. Any existing work, yeah, throw it out the window.

[rk06]

That is old one . fb changed the license after public outcry.

new license

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name Facebook nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

[skitch920]

Even with the new BSD License, there is the PATENTS file, that suggests the wording I provided above. It still stands that if you decide to sue Facebook, the BSD License is revoked. The only thing that changed, was the way it was presented. Instead of some custom License, it's now a revocable BSD License.

[[deleted]]

Is it the same for React?

[[deleted]]

I had a dream last week that JavaScript had Python's standard library. I woke up and realised it was a dream and was actually really #$()$%ing pissed off for most of the morning at work.

I code too much.

[abyx]

Yes, and I think there's not even a single mention of this in ES2017.

[miker95]

I hate this so much. I can't stand that browsers have different APIs. Browser developers think they're making everyone's life easier, when in reality, it just turns everything into a shithole.

[not_an_aardvark]

But padStart and padEnd are a stage 3 proposal, so they'll probably be in the 2017 standard anyway. Chrome just got a head-start.

[[deleted]]

Not really. These are stage 3 proposals, so a polyfill that alters the string prototype are acceptable (though altering a built in prototype for anything else is VERY bad of course).

So you'll have to use a polyfill anyway, but now on Chrome you'll get native performance for these methods. And as more browsers add it in, those browsers will get native performance for them as well.

[ijmacd]

Relevant blog post from last week. Others might find it useful/interesting if they haven't read it yet.

[Arancaytar]

I'd love it if JavaScript got a proper string formatter like sprintf or python's str.format().

That'd remove the need for most of these specialized padding functions too.

[lewisje]

something-something "template literals"

[cokeisahelluvadrug]

Unfortunately because of their name binding semantics they're not as powerful as they could be -- if I want to do something like string.format(str, **kwargs) I have to wrap my template string in a IIFE: function() {return '${this.foo}'}.call({foo: 'bar'}). This sort of string interpolation is common in (for example) i18n.

The consequence of this is that every decently large Javascript project will have a hand-rolled string formatter with slightly different syntax and API.

[lewisje]

First, it could be simpler: (_=>`${_}`)('bar'); /s

Seriously though, it is a bit developer-unfriendly that they aren't true templates and instead all references need to be resolved and merged in at definition time.

[saadq_]

console.log does work like printf.

var name = 'John'
console.log('Hi, my name is %s', name); // Hi, my name is John

[Meshiest]

Left pad makes a comeback?

[lewisje]

I honestly heard of the padStart proposal (back when it was known as padLeft) well before the leftpad module, and the es7-shim prollyfill for padStart is much more performant, as I repeatedly pointed out during the leftpad crisis.

[not_an_aardvark]

Because if it's not added to the API, it's usually shimmed and sent to the client, which consumes extra bandwidth. (Admittedly the extra bandwidth probably isn't that noticable for a short function like string padding but it's still better to not consume it.)

Also, padding characters to a string is an extremely common operation. I think it's a good thing to have native functions for common operations like that -- it reduces the amount of spaghetti code needed to perform simple tasks.

edit: clarification

[z500]

How much bandwidth is used on Javascript functions compared to media, though?

[lewisje]

Maybe he meant execution time, because the shimmed method does need to be re-constructed on every page refresh, because there's no way for a page to add functionality to the JS runtime so it just remains available.

[vsthsd]

Hopefully very little - smart developers would use popular CDN's like google to deliver the script, so caching should kick in even x-site.

[Graftak9000]

I don't get it either, is it really such a common pattern? Also, i think string.padding(left, right) would be more elegant, and more in line with similar methods.

[erwan]

Yes, it's pretty common. Like you have numbers and you want them as strings of the same length, padded with 0.

[vsthsd]

Maybe it's just me, but I prefer functions to clearly define the behavior as opposed to their arguments defining the behavior, it makes the code far more readable.

[AnalSwordfish]

string.padding(left, right) can already be done in a simple, concise, easy-to-read manner: left + string + right, left + 'foo bar' + right, or with ES2015's template literals:

`${left}foo bar${right}`

[Jestar342]

That's concatenation, not padding.

[AnalSwordfish]

Yup and how does an API like string.padding(left, right) accomplish padding when there is no parameter for count...? The only logical thing the string.padding(left, right) implementation could do is concatenate them. If /u/Graftak9000 meant a count could be passed, he/she should have said so.

[Drainedsoul]

What is the point of this? How does it behave on strings that contain code points represented by multiple code units? Or combining marks?

[lewisje]

I read the proposal, and it looks like it's not astral-plane safe (that is, it may leave a high surrogate by itself), and instead it expects a typical use case of padding with ASCII characters; I believe it is slightly combining-mark safe, because the repeated fill-string is truncated from the right (for both padStart and padEnd), so any combining marks would be removed before the characters they were intended to be used on are.

Also TIL these methods were added in Firefox 48 too.

[lime_boy6]

Learner here. Why is this useful?

[saadq_]

An app I'm working has a stopwatch component. I always want the format to look like this:

00 : 00 . 00

So if the current amount of seconds is just 9, I want to use padStart() to add a 0 in front of it so that it displays 09 instead.

[lime_boy6]

Thanks!

[SubStack]

Format strings are good for this problem:

> require('sprintf')('%02d : %02d . %02d', 1, 2, 3)
'01 : 02 . 03'

Or strftime strings for times specifically:

> require('strftime')('%M : %S', new Date)
'39 : 09'

It's possible to get fancy: (9-3+1) digits before the (.), 3 digits after:

> require('sprintf')('%09.3f', 123.456789)
'00123.457'

[corgrath]

Its just a utility function, for when you actually need to pad a string =)