Wow what a week! Last week’s challenge was a big hit. In case you missed it, here's a link to last week’s article here and the challenge on Coderby...
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I would not use WebAnimation API :
As for requestAnimationFrame, isn't it overkill too ?
I would use CSS transition for this kind of stuff.
The tricky part is to avoid reseting things at each call, so you need to:
Nice work!!
Maintaining state is not really that big of a deal using the webanimation api. The element's position is always a property of the element. Even though it wasn't asked of the question to maintain the final position, this is what the method could look like if that were a concern:
Still simpler. I would think the question should have also asked for units to be passed in as an argument to make it far more versatile.
I agree with you though! I would prefer to keep all animation logic in CSS. When I first read the question, I was thinking exactly about that, but I was also wondering what Facebook's goal might be in asking this question. Are they hoping the candidate to be aware of the built-in JS methods? If so, it's a good question to see how well the candidate is keeping his/her knowledge current. Or, maybe it's an opportunity for the candidate who is current to teach the interviewer something new. Is Facebook hoping the candidate to be able to do better than the built-in or will they get worried if the candidate goes down a rabbit hole? Etc.
Working example on jsfiddle
Update 12/11/2019: I provide a more complete example below (thanks to Vincent's reasoning)
Well actually it's more about building re-usable function you can use in every context (as a NPM package for example) than a real "Facebook Challenge" (who knows what they are really expecting from it ?)
The problem I can see from yours (even if it's a really simple solution) :
In fact, this one with same bugs can be rewritten with CSS transition in less lines and better browser support :
So yeah, WebAnimation API is powerful and awesome, but should always be used depending of the context (but It was quite fun to see an actual usage, thanks for it !)
Interesting perspective. I like the points you bring up! Fwiw, I think the API will eventually address those concerns, which I thought would have been addressed by now in 12/2019, but still being worked on (so yes, my mistake, my apologies). Future options I think will preserve state a bit better.
Wow interesting I didn’t know about it!
With future options it’s gonna be a real game-changer!
After giving this a bit more thought...I promise not to beat it death but...you led me on the right track and I created fully working code now (code review welcomed!). The one minor thing missed was that translateX alone won't always move the object to the right. I.e., if the object is rotated 45deg, the translateX will move along the rotated X axis, not to the right of the screen by the requested amount (i.e., 200px diagonally would mean sqrt((200)2 / 2) = 141 px to the right instead of 200px). The extra parameters need to be provided to the transformation matrix. So, they were really also testing us a bit on computational geometry, more than just the animation. With a few tweaks to the code, regardless of API used, the following code should still work regardless of initial transform:
Updated working examples are here: JSFiddle
(Alternative, using the MatrixAPI, is here. The
translateSelf
method had to be replaced withsetMatrixValue
)--> If the "test box" lines up with the "goal box" it passes.
I think this code addresses the key concerns that were brought up. I'd be damn impressed if someone could do this in a 15-minute phone screen! (and I'm pretty sure Facebook would be impressed by the questions you brought up!)
Awesome ! You did a really great job !
The only problem I see : they failed on 3D initial parameter (translateZ(1px)) :
So you need to make use of
matrix.is2D
(or check for/matrix3d/
to change the algorithm used but its seems quite painful to do.Here is a solution of the problem without the need of parsing the matrix data (just generate a 2D translation matrix and multiply it to the current matrix), with this solution you don't need to care about the 2D-3D stuff : jsfiddle.net/vthibault/9Lqyphkm/
I updated to include 3d, and also to account for when the animation ends, in case it's desired to chain the animation calls. I still prefer to directly set the parameters instead of performing the multiply operation (which can be a lot of multiply-add operations, and a potential source rounding errors if floating points are used).
Also, I think the
removeBackspaces
method can further be reduced withreduce
:Gives me the same result, I think, and helps guard against typical problems introduced by loops, such as "off-by-one" errors. (
array.reduce
helps the iteration stay within the bounds of the array size)For the Facebook question, just "cheat"...just create a wrapper around the built-in JS web-animation API and be done with it in 2 seconds (
elm.animate(...)
). The built-in isn't third party and technically not breaking directions...so...half cheating, I guess. No need to re-invent the wheel...Generally speaking, most interview questions are given despite well known methods / libraries being around that have already solved a problem! I have often been asked to implement lodash methods for example, even though in the real world, I'd just use lodash.
With a couple extra parameters.
Nice! Although this will move the element from a given position, rather than where it is on the page.
Thanks! Another fun challenge would be to add a timing function lerp, similar to cubic-bezier(x1, y1, x2, y2) to vary the speed over the course of the duration. It's a leap forward in complexity but quite doable.
This will only work if the element is absolute positioned.
Have you tried el.style.transform = "translate(x,y)"
My solution:
const animate = (element, miliseconds, distance) =>{
element.style.transition =
all ${miliseconds/1000}s ease
;element.style.transform =
translateX(${distance}px)
;}
animate(document.querySelector('div'), 2000, 100)
This is what I got.
I think the challenge is asking if you know how to use requestanimationframe basically.
But that is crazy overkill for this task. The appropriate way to implement this in current year is to use CSS. If an animation can be done without issue in CSS you should never use JS to do it. That is actually kind of a good rule to extrapolate and follow for everything on the front-end: Use JS only for the things you can't do with other technologies.
Good point!
And, just a helpful link: Passing Parameters to CSS animation if anyone is interested... this would be the CSS way of doing it. JS events fire (like "scrolling", "mousemove") and the data from those events get passed to the css vars (but maybe someday we'd find it easier to pass an argument to a method in JS instead? easier to test maybe?). I think the webanimations API will surprise us all in [1-2 years?] and challenge us all as to what we do in JS vs CSS. I could be wrong. I'm still thinking about the pros and cons.
Nice solution!