如何解释Crockford的JavaScript Trim函数？

Question

I'm going through the JavaScript Programming Language series by Douglas Crockford and came across this expression in his trim function:

String.prototype.trim = function () {
  return this.replace(/^\s*(\S*(\s+\S+)*)\s*$/, "$1");
};

I get what it does but how in the world does it work?

Answer 1

You should grab a tool like expresso , where you can step through the regex...

^\\s* - Whitespace at the beginning of the line or string, with any number of repetitions

(\\S*(\\s+\\S+)*) - Capture group, number "$1" in your example.

\\S*(\\s+\\S+)* - Anything but whitespace, any number of repetions

(\\s+\\S+)* - Another capture group, which looks for whitespace with one or more repetitions and anything other than whitespace with one or more repetitions.

\\s*$ - Any number of whitespaces at the end of the line or string.

What it looks like in Expresso...