为什么 javascript 执行时间每次都不同？

Question

If the code is exactly the same every time it runs, why didn't it use exact same amount of execution time?

For example, code as simple as:

console.time();
console.timeEnd();

would yield different result every time I run it.

Answer 1

To understand why it is so, first of all you should know JS works in conurrency model. There is event loop in Javascript which is responsible for executing the JS code. So this reference will definitely help to answer this question.

Answer 2

There are lots of things happening that use memory in your computer while you have your browser open and your script is running. Those things affect how much memory your browser has access to. The more memory your browser has available at that time, the faster your script will run.