使用CSS和JS动态设置div尺寸时，如何补偿更长的加载时间？

Question

I am creating a Polymer app which displays information in rows in a custom element "table". I am using polymer flexbox classes to initially position elements. I need to take measurements with JS after the elements have loaded and assign widths to elements in the table accordingly. The problem goes something like this:

row 1
*--------------------*
|       *-----------*|
|       |    el a   ||
|       *-----------*|
*--------------------*
row 2
*--------------------*
|            *------*|
|            | el b ||
|            *------*|
*--------------------*

Row 1 and row 2 have fixed widths, but el a or b could be of any width. Regardless of contents of el a or b , I want the el's contained in the rows to be all the same width as the widest. So in this case, a is widest so el b should adjust its width to match a .

I am using polymers attached method to ensure the elements are loaded before taking scrollWidth measurements via JS. I initially ran into the problem of getting undefined elements when I tried to grab them with querySelector , but I fixed this using Polymer's async . I can style the elements fine in a modern browser just fine. Consider the following code.

attached: {
  this.async(function() {
    console.log(Polymer.dom(this.root).querySelector('#a').scrollWidth);
    console.log(Polymer.dom(this.root).querySelector('#b').scrollWidth);
  }, 100);
}

A modern version of chrome will return something like 100px for a and 60px for b . If I test an older version of chrome or a different browser like firefox, a and b will be 5-15px less than what modern chrome measured. I found out that if I increase the async time enough, no matter the age of the browser, I will eventually get a measurement matching what modern chrome returned. This is to say while it appears the div exists on the page and I can grab it with querySelector , it seems to be fluctuating so that it is not at its full width yet.

I don't like guessing how long it will take for the elements to fully load before I can take measurements. I am trying to figure out a way I can be 100% confident that the elements are done loading or perhaps an alternate method of styling these elements I have overlooked. I have had the most success with using setTimeout on the function that is doing the measuring and waiting for it to measure the same thing several times in a row. But even that has been inconsistent at times and occasionally b will be slightly less wide than a when the web page appears.

Answer 1

One option when you need to keep checking things, even if it's been true a couple times, is to continue to use setTimeout infinitely until the values are no longer changing for a certian # of iterations. For example, if they are still the same after 10 timeouts, stop the timeouts from going all together.

something like...

var count = 0;
function check() {
   do_something();
   if (same_as_last_time == true) {count++}
   if (count < 10) setTimeout (check,100);
}
setTimeout (check,100);

Although this could be wildly inefficient and possibly ineffective depending on how staggered your data is appearing.

I believe the actual solution here lies in the fact that you are using the variable ".scrollWidth" as your measurement point, which is a terrible measurement to standardize your widths across browsers. See this SO post for more info on that ( https://stackoverflow.com/a/33672058/3479741 )

I would recommend instead using a different method of acquiring the width and compare to see whether your results are more consistent. There are many options that remain more consistent than ".scrollWidth" in the article above.