Idle Until Urgent

https://philipwalton.com/articles/idle-until-urgent/

by bootslebaron • 8 years ago

295 83 8 years ago

jgtrosh• 8 years ago

Reading this article and applying a similar technique to a different webpage could be a good exercise for advanced students in front end development. The core idea is put forward, and no implementation detail is left out; great article.

thegeomaster2• 8 years ago

What I don't understand is why a very simple blog like this needs a ~56KB bundle of JavaScript at all.

Cthulhu_2• 8 years ago

^ exactly; blogs are mostly static. You can improve the responsiveness of e.g. a comments section with a bit of JS, but that's very low priority and doesn't need to be much.

oftenwrong• 8 years ago

This blog works fine without javascript.

pc86• 8 years ago

Which doesn't answer the question.

mrspeaker• 8 years ago

Looking at the blog post, I'd say it was for drawer.init(), contentLoader.init(), breakpoints.init(), alerts.init(), and analytics.init(). The site works fine without javascript, so it doesn't need it - perhaps the author thinks the 50k is worth the drawer, content loading, breakpoint?, and alert features and also wants a bit of user analytics tracking.

AstralStorm3• 8 years ago

Even so, you could backload the drawer etc. placing them at the end of the document and attaching to potentially already rendered page.

Reorder so that your main content loads first.

Author did part of it by deferring the analytics init. Not sure why they used setTimeout though for the initialization instead of requestIdleTimeout like everything else. The page is supposed to work without JS after all.

"I mentioned above that requestIdleCallback() doesn’t come with any guarantees that the callback will ever run."

Not true - there's a timeout argument. It guarantees that the callback will by ran by then.

mjdease• 8 years ago

Regardless of the demonstrated use case, these principles can be applied to improve the performance of web pages that use JavaScript

CydeWeys• 8 years ago

Thank you. That'd be like someone criticizing a coding example for a new language saying "What's the point of using OOP for implementing Tic-Tac-Toe? It's too simple to necessitate it."

ummonk• 8 years ago

You make that sound like a lot. It's only equivalent to like 20 pages of raw plain text in size.

neetdavid• 8 years ago

I poked around a little and it seemed like the majority of it is related to analytics events (googleanalytics/autotrack)

I suppose the author just wants to know a little about how their blog and writing is performing in the wild

Sort of off topic, but it would be interesting if the browser handled these common cases instead and gave the user a way to opt-in/out. I suppose it sort of does by broadcasting those events to the js listeners in the first place.

AstralStorm3• 8 years ago

I'm not sure why you trust Google Web "Fundamentals" that 0-100ms is perceived as instant.

The upper bound is perceptibly laggy. I have no idea where Google took their numbers from.

FID of 100 ms is already bad as you have to add network latencies on top of it.

To put things into perspective, it's more than the time it takes to fully boot embedded Linux as coreboot from not too fast flash or start up Commodore 64 with a good extension cartridge.

The browsers are terribly slow.

treerock• 8 years ago

r.e. the 100ms, some references are given on this stackoverflow question.

https://stackoverflow.com/questions/536300/what-is-the-short...

Xichom2k5• 8 years ago

I don't think scroll gestures or incrementally-loaded content with layout reflows were a thing back then, so that might need re-evaluating.

jcelerier3• 8 years ago

...a team of neuroscientists from MIT has found that the human brain can process entire images that the eye sees for as little as 13 milliseconds...That speed is far faster than the 100 milliseconds suggested by previous studies...

davemp• 8 years ago

The rule of thumb I've seen used in the embedded world is 50ms latency for user input and I found that it's still noticeable vs say 25ms.

taneq3• 8 years ago

Getting offtopic here but arguably the best thing about the growing prevalence of VR is that it's forcing everyone to focus on maximum latency rather than frame throughput, and so that godawful stutter is finally being exorcised from our rendering stacks.

tbrock• 8 years ago

I’ve always believed that the 100ms figure includes network round trip time.

espeed• 8 years ago

I'm not sure why you trust Google Web "Fundamentals" that 0-100ms is perceived as instant.

Those numbers go back to the studies Jakob Nielsen did at the Sun Microsystems usability lab and the results posted in his oft cited AlertBox articles from 1993 and 1997...

https://www.nngroup.com/articles/website-response-times/

dragonwriter• 8 years ago

Those numbers go back to the studies Jakob Nielsen did at the Sun Microsystems usability lab and the results posted in his oft cited AlertBox articles from 1993 and 1997...

Actually, Nielsen indicates that had already been a consistent finding for ~30 years at that point, citing “Response time in man-computer conversational transactions” (Miller, 1968) [0] as the original source.

[0] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=Resp...

bluquark• 8 years ago

100ms is slightly arbitrary, but the real point of saying "100ms" is that it's lower than the multiple seconds typically required for page load, and higher than the 16ms required for smooth animation. An appropriate target for input response time (the "R" in RAIL) is somewhere in between those two.

If 100ms strikes you as too high, then by all means target a lower number like 50ms. But it's still not a disaster if your 95th percentile is 100ms. Also, if your A time is above 16ms or your L time is above 5 seconds, your limited development time might be better spent improving those rather than bringing R down even further.

iofiiiiiiiii• 8 years ago

Not being a JavaScript guy, my eyes sort of glazed over after the flame graphs. Do I understand the gist of it right that a 200+ millisecond delay is normal if you just have 56KB of light blog page style JavaScript code whose loading you do not somehow optimize? Or is there something pathological in play here?

alanning• 8 years ago

It depends on what the JavaScript code is doing.

The article discusses an example where code is loading Intl.DateTimeFormat which takes some time but is not immediately used.

So if the 56KB code doesn’t do a lot of loading of expensive components then it may not need further optimization, although it may still have the problem of blocking user input.

Main moral of the story is you can’t assume performance based on code size, you have to measure.

a012• 8 years ago

Meanwhile, there are many websites don't care if their page loads in a few seconds. For example: https://i.imgur.com/coBKPa1.jpg

theandrewbailey• 8 years ago

I guess I'm an old man that hasn't smoked the hype, but I don't understand why one would write this:

    const main = () => {
        setTimeout(() => drawer.init(), 0);
        setTimeout(() => contentLoader.init(), 0);
        setTimeout(() => breakpoints.init(), 0);
        setTimeout(() => alerts.init(), 0);
        requestIdleCallback(() => analytics.init());
    };

over this:

    function main(){
        setTimeout(drawer.init, 0);
        setTimeout(contentLoader.init, 0);
        setTimeout(breakpoints.init, 0);
        setTimeout(alerts.init, 0);
        requestIdleCallback(analytics.init);
    };

streptomycin• 8 years ago

The 2nd style will not work if those functions internally use `this` and were not previously manually bound to their parent objects, like `drawer.init.bind(drawer)`.

taneq3• 8 years ago

Presumably if you were going to write the latter, you'd also write your init() functions accordingly?

Xichom2k5• 8 years ago

Due to javascript's funky notion of object methods. If you just pass the function reference itself invoking it will execute it with a |this| set to undefined.

Put differently, a property access x = foo.bar followed by x() is not the same as foo.bar()

avip2• 8 years ago

The default this context would be the global window object (in the browser).

avip2• 8 years ago

This.

ak39• 8 years ago

How long have you waited for this?

ealhad3• 8 years ago

I can't figure out if the pun was intended.

Cthulhu_2• 8 years ago

The second argument (0) is also optional, 0 is the default value.

rbonvall• 8 years ago

JavaScript is a minefield of unexpected behavior when you try things like this. Besides the issue with this-binding already mentioned in the thread, there are other examples of weird stuff that happens when you don't introduce an apparently redundant lambda:

    > ['10', '10', '10', '10', '10'].map(parseInt)
    [ 10, NaN, 2, 3, 4 ]

    > ['10', '10', '10', '10', '10'].map(x => parseInt(x))
    [ 10, 10, 10, 10, 10 ]

jcelerier3• 8 years ago

I'll take C++ UB every day over this

infogulch• 8 years ago

Ok this was a 'wat' moment for me until I realized that map passes up to 3 args to the function, including index, and parseint accepts a radix parameter. Still kinda weird/unintuitive, I could see myself not paying attention and reducing to the first example accidentally.

kristjansson• 8 years ago

I’ve heard something about a surprise principle in API design. Principle of most surprise I think it was? Let’s go with that.

The design process of this, I imagine.

bovermyer• 8 years ago

While this is impressive work, I can't help but wonder if this is solving the wrong problem.

If the goal is to load fast, wouldn't it be better to just stop using JavaScript altogether? It's a blog, not an app.

alangpierce2• 8 years ago

I don't think the author is suggesting that people should put this much effort into optimizing their blog. It's a toy example that's simple enough to explain concepts that can then be applied to bigger and more complex webapps where "don't use JavaScript" isn't an option, like with the Redux example mentioned further down in the article.

enobrev• 8 years ago

I don't think this comment matters, but since so many other comments on this article are speaking up against, maybe it does.

I don't care, at all whatsoever, if this person wants to use JavaScript for their blog.

Otherwise, nice article about improving performance and prioritizing important functionality during page-load.

craftyguy• 8 years ago

I don't care, at all whatsoever, if this person wants to use JavaScript for their blog.

In most cases complaining about this is 'offtopic', but in this case it is very much on-topic since the blog is about optimizing javascript usage.

I'm just happy that you can actually read what they have to say without JS enabled!

code-is-code• 8 years ago

A few month ago, I used a similar optimisation that does the same idle-awaiting but with server-requests instead of cpu-usage. So instead of submitting all ajax to the server directly, background tasks can be delayed until the important tasks have finished. This is useful especially when the 6 requests per origin limit gets hit often.

https://github.com/pubkey/custom-idle-queue

alangpierce2• 8 years ago

Important! While browsers can run input callbacks ahead of queued tasks, they cannot run input callbacks ahead of queued microtasks. And since promises and async functions run as microtasks, converting your sync code to promise-based code will not prevent it from blocking user input!

Wow, my initial reaction while reading was "just use async functions and then then code will naturally allow user input in the middle", good to know that that doesn't work.

hinkley3• 8 years ago

This is slowly turning into a rock in my shoe. You would think a single threaded language would implement some sort of cooperative multitasking scheme. But promises aren’t cooperative, especially in Bluebird (the queue management logic was converted to LIFO a long time ago, although that code still contained comments or variable names that imply the opposite, when last I looked).

I’m tempted to call this the legacy of Brendan “design a language in a week” Eich, but that would let too many other people off the hook.

IMO, webasm can’t happen fast enough.

paulddraper4• 8 years ago

But promises aren’t cooperative

Promises are cooperative.

You cannot interrupt execution (unlike, say, preemptible threads).

You can only perform other execution when the current execution terminates or yields, e.g. with await.

---

I think you are wanting browser UI events to preempt between Promises/microtasks.

That's fair enough, but saying that Promise aren't cooperative is the wrong description.

Xichom2k5• 8 years ago

You can yield back to the UI event loop in an async function through

   await new Promise((resolve) => setImmediate(resolve))

or similar constructs using setTimeout or requestAnimationFrame

paulddraper4• 8 years ago

Correct.

Though setImmediate is specific to IE/Edge.

    setTimeout(resolve, 0)

will allow any queued events/macrotasks to occur, and then immediately resolve.

    requireAnimationFrame(resolve)

will wait until the browser is ready to render another frame, and then resolve.

Touche• 8 years ago

Yeah this is often misunderstood. Instead of thinking that promises make your code "run later" it's better to think about it as reorganizing still-synchronous code.

elfakyn• 8 years ago

The Amazon app has an absolutely horrendous FID of around 10 seconds or so. They could use a little bit of optimization.

sequoia2• 8 years ago

[cw: tangential point]

This is the JavaScript equivalent of death by a thousand cuts.

Seems to me there's one really big knife in particular, doling out most of the cuts: https://i.imgur.com/Hzrfq13.png

I wonder what analytics platform is contributing all this slow-down to his first interaction... ;)

philipwalton4• 8 years ago

Article author here. Yep, not hiding that fact (I could have easily used a trace with minified code, but I didn't to point this out).

Two things though:

1. I used to work on Google Analytics, and I've created a lot of open source libraries around Google Analytics, which I use on my own site because I like to test my own libraries (and feel any pain they may be causing). The way most people use Google Analytics does not block for nearly this long.

2. I've updated my Google Analytics libraries to take advantage of this strategy [1], and I'm working with some of my old teams internally to see if they can bake it in to GA's core analytics.js library, because I strongly believe that analytics code should never degrade the user experience.

[1] https://github.com/googleanalytics/autotrack/pull/235

sequoia2• 8 years ago

Yep, not hiding that fact (I could have easily used a trace with minified code, but I didn't to point this out).

Kudos to you for your honesty here! I was a bit confused by your question "So what’s taking so long to run?" when it seemed pretty clear what was taking so long to run. If the goal were simply "speed up the pageload/FID", removing browser analytics (in favor of server e.g.) would seem to be at least an _option_ to immediately achieve that end.

Thanks for the article.

jschwartzi2• 8 years ago

If I had a nickel for every timea page load was blocked connecting to an analytics platform I would be able to retire.

eridius• 8 years ago

If the measurement here is how long it takes to respond to the first user input, why does a 233ms main function matter? As a user, how am I expected to scan the page, locate a link, and click on it within that 233ms?

jschwartzi2• 8 years ago

Imagine that his site was linked somewhere else. In that scenario it takes 233ms from click to display. That's why this matters, because users aren't opening a browser to that one page. They're clicking around on different pages, and if each one takes 233ms that's a very slow process.

benjaminjackman• 8 years ago

Here is:

- The [repo](https://github.com/GoogleChromeLabs/idlize) implementing the pattern described in the article

- The [package](https://yarnpkg.com/en/package/idlize)

Idle Until Urgent

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