当我需要顶部的函数时，为什么我的脚本中的某些点没有定义函数? [英] Why is a function not defined at certain points in my script when I am requiring the function at the top?

问题描述

我正在使用 Javascript 制作游戏.我使用 webpack 来捆绑我的模块，所以在每个 Javascript 文件的末尾我使用 module.exports.下面是一个例子:

I am making a game using Javascript. I use webpack to bundle my modules, so at the end of each Javascript file I use module.exports. Here is an example:

//spaceship.js
var Spaceship = function(options) {
  this.position = options.position
  this.name = options.name
}

module.exports = Spaceship


//game.js
var Spaceship = require("./spaceship");

var Game = function() {
  this.num_spaceships = 5;
  this.spaceships = [];
  // DEBUGGER 1
  this.add_spaceships();
}

Game.prototype.add_spaceships = function() {
  // DEBUGGER 2
  for(var i = 0; i < this.num_spaceships; i++) {
    this.spaceships.push(this.randomSpaceship
  }
}

Game.prototype.randomSpaceship = function() {
  //DEBUGGER 3
}

在上面的每个调试点，如果我打开 Chrome 开发工具并输入 Spaceship 我得到 Uncaught ReferenceError: Spaceship is not defined(...)

At each of the debugging points above, if I open Chrome dev tools and type in Spaceship I get Uncaught ReferenceError: Spaceship is not defined(…)

如果我改变函数 randomSpaceship 如下:

If I change function randomSpaceship as follows:

Game.prototype.randomSpaceship = function() {
  //DEBUGGER 3
  var s = new Spaceship();
}

然后在 DEBUGGER 3 中，Spaceship 现已定义(如果我打开开发工具，我会发现 Spaceship 是一个函数).

Then at DEBUGGER 3, Spaceship is now defined (if I open dev tools I get that Spaceship is a function).

为什么会这样?我想它可能与变量提升有关，但我在文件 game.js 的顶部声明并分配了变量 Spaceship.

Why does this happen? I imagined it could have something to do with variable hoisting perhaps, but I am declaring and assigning the variable Spaceship at the top of the file game.js.

推荐答案

发生这种情况是因为您没有在 Game 和 add_spaceships 中使用 Spaceship 变量code> 函数位于 DEBUGGER 1 和 DEBUGGER 2 调试点所在的位置，因此 Chrome 不会在闭包中捕获此变量.在 DEBUGGER 3 中，你使用了变量，所以它被捕获在一个闭包中，你可以检查它.

This happens because you don't use Spaceship variable inside Game and add_spaceships functions where DEBUGGER 1 and DEBUGGER 2 debugging points are located and so Chrome doesn't capture this variable in closure. In DEBUGGER 3 you use the variable and so it's captured in a closure and you can inspect it.

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