零作为IIFE中的第一个参数 [英] Zero as first argument in IIFE

问题描述

在babeljs v6.5.1中，

class Foo {}

编译为

"use strict";

var _classCallCheck2 = require("babel-runtime/helpers/classCallCheck");

var _classCallCheck3 = _interopRequireDefault(_classCallCheck2);

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

var Foo = function Foo() {
  (0, _classCallCheck3.default)(this, Foo);
};

(0, _classCallCheck3.default)(this, Foo);中0的意义是什么?

在在线

In the online babeljs repl, which probably has a different babeljs version, that line is simply _classCallCheck(this, Foo);, and they seem to do the same thing. What's the difference between these two statements?

推荐答案

0被忽略.仅允许逗号运算符对_classCallCheck3.default求值并获得函数而无需this是_classCallCheck3.

The 0 is ignored. It is there solely to allow the comma operator to evaluate _classCallCheck3.default and get the function without this being _classCallCheck3.

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