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javascript - Babelifying JavaScript Module Pattern with ES6 Arrow Functions

问题描述

Babel is choking on code that uses the module pattern with an arrow function.

If I try to process a file which reads:

const lib = (() => {
  function sum(a, b)  { return a + b; }
  function mult(a, b) { return a * b; }

  return {
    sum,
    mult
  };
}());

Babel gives a SyntaxError

{ SyntaxError: /home/david/Sync/ebs/office/fake.js: Unexpected token, expected "," (9:1)

   7 |     mult
   8 |   };
>  9 | }());
     |  ^
  10 | 
    at Parser.raise (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:3939:15)
    at Parser.unexpected (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:5248:16)
    at Parser.expect (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:5236:28)
    at Parser.parseParenAndDistinguishExpression (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:6454:14)
    at Parser.parseExprAtom (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:6284:21)
    at Parser.parseExprSubscripts (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:5924:21)
    at Parser.parseMaybeUnary (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:5903:21)
    at Parser.parseExprOps (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:5812:21)
    at Parser.parseMaybeConditional (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:5784:21)
    at Parser.parseMaybeAssign (/home/david/Sync/ebs/office/node_modules/@babel/parser/lib/index.js:5731:21)
  pos: 137,
  loc: Position { line: 9, column: 1 },
  code: 'BABEL_PARSE_ERROR' }

However, if I change the code to use an older style function, like

const lib = (function () {
  function sum(a, b)  { return a + b; }
  function mult(a, b) { return a * b; }

  return {
    sum,
    mult
  };
}());

Babel seems to process the file with no issues.

What am I doing wrong? Is there a genuine syntax problem with the arrow function code I am not aware of?

标签： javascriptecmascript-6babeljsmodule-patternrevealing-module-pattern

解决方案

由于箭头函数的性质以及它们的解释方式，（例如：

const x = () => ({ objectPropValues });
const x = () => { functionBody };
const x = () => conciseFunctionBody;

我想第二个箭头功能在

const x = (() => {functionBody})();
const x = (() => {functionBody}());

不能被允许，也不能。

这可以通过仔细查看 ECMA 6 的箭头函数规范来确认。

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