JavaScript 字符串拆分：固定宽度与分隔性能

Question

I am building a string to be parsed into an array by JavaScript. I can make it delimited or I can make the fields fixed-width. To test it, I built this jsperf test using a data string where the fields are both fixed-width and comma-delimited:

https://jsperf.com/string-split-fixed

I have only tested on Windows with Firefox and Chrome, so please run the test from other OSes and browsers. My two test results are clear: String.prototype.split() is the winner by a large margin.

Is my fixed-width code not efficient enough, or is the built-in string split function simply superior? Is there a way to code it so that the fixed-width parsing triumphs? If this was C/C++, the fixed-width code, written properly, would be the clear winner. But I know JavaScript is an entirely different beast.

Answer 1

String.prototype.split() is a built-in JavaScript function. Expect it to be highly optimized for the particular JS engine and be written not in JavaScript but in C++.

It should thus not come a surprise that you can't match its performance with pure JavaScript code.

String operations like splitting a delimited string are inherently memory-bound. Hence, knowing the location of delimiters doesn't really help much, since the entire string still needs to be traversed at least once (to copy the delimited fragments). Fixed-position splitting might be faster for strings that exceed D-cache size, but your string is just 13KB long, so traversing it multiple times isn't going to matter.