Throw Expressions (Stage 2)

[hzoo]

Champions: Ron Buckton (@rbuckton)
Spec Repo: https://github.com/rbuckton/proposal-throw-expressions
First presented at the July 2017 meeting: https://github.com/tc39/agendas/blob/master/2017/07.md
Stage 1 to Stage 2 at Sept 2017 meeting

Examples:

function save(filename = throw new TypeError("Argument required")) {}

lint(ast, { 
  with: () => throw new Error("avoid using 'with' statements.")
});

function getEncoder(encoding) {
  const encoder = encoding === "utf8" ? new UTF8Encoder() 
                : encoding === "utf16le" ? new UTF16Encoder(false) 
                : encoding === "utf16be" ? new UTF16Encoder(true) 
                : throw new Error("Unsupported encoding");
}

class Product {
  get id() { return this._id; }
  set id(value) { this._id = value || throw new Error("Invalid value"); }
}

Implementation

• Parser
• Transform
• TS: Support for the ECMAScript 'throw' operator microsoft/TypeScript#18798
• REPL: https://babeljs.io/repl/build/master#?&browsers=&build=&code_lz=DYSwdgLgFAhgzhANAAgN7IFDOQdxBACwC5koBKZAXgD5lCAnAex2TAFMWBRep-qAIhgA3RiAAmyAK5xwAc2QByPIQXIEMCGwC2bSHAB0_MhgC-ZANwYgA&circleciRepo=&lineWrap=true&presets=stage-0&targets=&version=7.0.0-beta.2

[ljharb]

Note there's an open question on throw x, y as well as its precedence, so you may want to hold off on implementing this.

[jridgewell]

Babylon: babel/babylon#740

[jridgewell]

Babel: babel/babel#6325

[hzoo]

Ok merged the parser/plugin and moved to Stage 2 preset in master

[jridgewell]

Can you add to proposals readme?