Add trim/trimStart/trimEnd to string prototype

[lennartbuit]

Hey there, I saw your JSConf talk about writing a toy JS engine, and I wanted to contribute. I am not very experienced in Rust, so bear with me :)!

---

I implemented trim/trimEnd/trimStart to get my toes wet, which are part of #13.

There is a subtle difference in what Rust regards whitespace, and what is considered whitespace in the ECMAScript language. From what I could gather in both languages, it appears that Rust does consider U+0085 (next line) as whitespace but not U+FEFF (zero width non-breaking space), and vice versa for ECMAScript.

I wrote a bit of JavaScript to compare to the v8 impl, all console logs should print true[1]:

function testTrim(ws_char) {
  let str = new String(ws_char + 'abc' + ws_char);
  let trimmed = str.trim();
  console.log(trimmed.length == 3);
}

// Explicit whitespace
testTrim('\u0009');
testTrim('\u000B');
testTrim('\u000C');
testTrim('\u0020');
testTrim('\u00A0');
testTrim('\uFEFF');
// Space sep whitespace
testTrim('\u0020');
testTrim('\u00A0');
testTrim('\u1680');
testTrim('\u2000');
testTrim('\u2001');
testTrim('\u2002');
testTrim('\u2003');
testTrim('\u2004');
testTrim('\u2005');
testTrim('\u2006');
testTrim('\u2007');
testTrim('\u2008');
testTrim('\u2009');
testTrim('\u200A');
testTrim('\u202F');
testTrim('\u205F');
testTrim('\u3000');
// Line terminators
testTrim('\u000A');
testTrim('\u000D');
testTrim('\u2028');
testTrim('\u2029');

Feedback more than welcome!

[1]: Not very pretty JavaScript, but it works in boa :). Implementing Array.prototype.map was too much work for an initial contribution ;)

[jasonwilliams]

This is awesome work @lennartbuit!
thanks for the contribution, will take a look.

[jasonwilliams]

Works great, would be good to setup some testing harness for these changes

[lennartbuit]

I agree, I did take a peek at the test262 harness and/or providing rust based unit tests, but didn't know how to. So thats why I resided to the javascript above.

I am hopeful I can contribute some more this weekend as long as you are willing to tolerate my clear lack of experience in Rust :). Any good 'one Sunday' sized suggestions? Otherwise I'll just fill in another blank of the string prototype :)!