Only Mozilla supports JavaScript (which is a mix of JavaScript-only features and ECMAScript; it's a little complicated), and everyone else implements ECMAScript

Only Mozilla supports JavaScript (which is a mix of JavaScript-only features and ECMAScript; it's a little complicated), and everyone else implements ECMAScript. Some JavaScript features are in discussion of being added to ECMAScript, but no current ECMAScript engines (e.g. V8) have implemented them yet, barring the partial destructuring assignment implementation supported by Opera's Futhark ECMAScript engine.