Question

我试图在关于模块的部分中使用Eloquent Javascript运行这个简短的程序。

var weekDay = function() {}();

(function(exports) {
  var names = ["Sunday", "Monday", "Tuesday", "Wednesday",
    "Thursday", "Friday", "Saturday"];

  exports.name = function(number) {
    return names[number];
  };
  exports.number = function(name) {
    return names.indexOf(name);
  };
})(this.weekDay = {});

console.log(weekDay.name(weekDay.number("Saturday")));

正确的输出应为// -> Saturday。

它在浏览器中完美运行。但是，当我尝试在Node解释器中运行它时，我收到此错误：

TypeError: Cannot read property 'name' of undefined

我只能假设它与Node处理exports关键字的方式有关。有人可以帮助我至少粗略地理解这种行为吗？

Answer 1

Nir Levy的答案是正确的，但我也发布了这个答案，因为你在谈论模块。这就是你如何制作一段代码的模块。

//create your module like this and put this module in a separate file (ex. weekDay.js)
var weekDay = (function() {
  var names = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];

  var name = function(number) {
    return names[number];
  };
  var number = function(name) {
    return names.indexOf(name);
  };

  return {
    number: number,
    name: name
  } 
})(); //it's a self executing function

//exporte module
module.exports = weekDay



//to get your module (in another file)
var weekDayModule = require('./weekDay'); //path to module

console.log(weekDayModule.name(weekDayModule.number('Saturday')));

Answer 2

在node.js这一行：

var weekDay = function() {}();

只生成一个未定义的变量weekDay，因为它所做的只是定义一个en空体（代码中为{}）的函数并立即运行它。由于正文是空的（最重要的是，没有返回语句），因此它会产生未定义的

执行所需操作的方法是将整个定义放在此函数中，并定义要公开的内容，如下所示：

var weekDay = function() {
  var names = ["Sunday", "Monday", "Tuesday", "Wednesday",
    "Thursday", "Friday", "Saturday"];

  var name = function(number) {
    return names[number];
  };
  var number = function(name) {
    return names.indexOf(name);
  };

  return {
    number: number,
    name: name
  }

}();


console.log(weekDay.name(weekDay.number("Saturday")));

Answer 3

将第一行更改为var weekDay = {};，当你调用你的生命时，只需将你在第一行创建的内容放入其中。

Javascript - 在Node.js和浏览器中导出

3 个答案: