ECMAScript proposal, specs, tests, and reference implementation for String.prototype.trimStart/trimEnd (plus trimLeft/trimRight).

ES5 standardized String.prototype.trim. All major engines have also implemented corresponding trimLeft and trimRight functions - without any standard specification. For consistency with padStart/padEnd we propose trimStart and trimEnd and trimLeft/trimRight as aliases required for web compatibility.

You can view the spec in ecmarkup or rendered as HTML.

For consistency with padStart/padEnd the standard functions will be trimStart and trimEnd, however for web compatilibity trimLeft will alias trimStart and trimRight will alias trimEnd. This means String.prototype.trimRight.name will change from "trimRight" to "trimEnd" in most engines. The spec author does not expect this to cause any breakage.

PR open

This initial proposal was drafted by @sebmarkbage and the updated spec was drafted by @evilpie with input from @ljharb.

This proposal is currently at stage 3 of the process.

Designated TC39 reviewers: Jordan Harband + Daniel Ehrenberg

• V8, in Chrome 66+
• SpiderMonkey, in Firefox 61+