Zero as first argument in IIFE [duplicate]

问题:

This question already has answers here:

Why does babel rewrite imported function call to (0, fn)(…)? (2 answers)

Closed 4 years ago.

In babeljs v6.5.1,

class Foo {}

compiles to

"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);
};

What's the point of the 0 in (0, _classCallCheck3.default)(this, Foo);?

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?

回答1:

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.