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December 20, 2015 19:29
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To understand the whole 4ms clamping situation
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| <!DOCTYPE html> | |
| <html lang="en"> | |
| <head> | |
| <meta charset="utf-8"> | |
| <script> | |
| var MAX = 10; | |
| var i = 0; | |
| var times = []; | |
| var now = performance.now.bind(performance) | |
| setTimeout(function f(){ | |
| times[i] = now(); | |
| if(i < MAX){ | |
| setTimeout(f, 0); | |
| i++; | |
| } | |
| else{ | |
| console.log( times.reduce(function(acc, curr, i){ | |
| if(i === 0) | |
| return acc; | |
| acc.push(curr - times[i-1]) | |
| return acc; | |
| }, []) ); | |
| } | |
| }, 100); | |
| </script> | |
| <title> TITLE </title> | |
| </head> | |
| <body> | |
| </body> | |
| </html> |
Background story: last week, @DavidBruant’s tweet made me wonder… If setTimeout(f, 0) actually runs as soon as possible (no 4ms clamping), then why is the LawnMark benchmark affected by it?
Online version: https://rawgithub.com/DavidBruant/6183351/raw/e44545406b3fa125e8ff7e0453226abb767ec2d2/setTimeoutClamping.html
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Open this in a browser. In your console, you should notice that the 4 first timestamps are really close to one another (as close to what the browser can make them). Each following timestamp is separated from at least 4ms to the previous one.