JavaScript 闭包(this)

Question

这个问题已经有答案了:

Methods in ES6 objects: using arrow functions (6 个回答)

已关闭 6 年前。

我已经在 stackoverflow 上到处查找，但找不到任何答案。

未捕获的类型错误:this.rsGame 不是一个函数(与 this.addEnemy 相同)

let game = new Phaser.Game(600,600);
let speed = 500;


let scyla = {

    preload: () => {
      game.load.image('bg', 'assets/bg.png');
      game.load.image('pl', 'assets/pl.png');
      game.load.image('enemy', 'assets/enemy.png');

    },
    create: () => {

      game.physics.startSystem(Phaser.Physics.ARCADE)

      game.add.sprite(0,0, 'bg');

      this.player = game.add.sprite(300, 500, 'pl');
      this.player.anchor.set(0.5);

      game.physics.arcade.enable(this.player);
      this.cursors = game.input.keyboard.createCursorKeys();

      this.enemies = game.add.group();

      // this.timer = game.time.events.loop(200, this.addEnemy(), this);
    },
    update: () => {

      this.player.body.velocity.x = 0;
      this.player.body.velocity.y = 0;

      if (this.cursors.left.isDown)
          this.player.body.velocity.x = speed * -1;

      if (this.cursors.right.isDown)
          this.player.body.velocity.x = speed;

      if (this.cursors.up.isDown)
          this.player.body.velocity.y = speed * -1;

      if (this.cursors.down.isDown)
          this.player.body.velocity.y = speed;

      if (this.player.inWorld === false)
          this.rsGame(); 
    },
    rsGame: () => {
      game.state.start('scyla');

    },
    addEnemy: () => {
      let enemy = game.add.sprite(300, 100, 'enemy');
      game.physics.arcade.enable(enemy);
      enemy.body.gravity.y = 200;

      this.enemies.add(enemy);
      enemy.checkWorldBounds = true;
      enemy.outOfBoundsKill = true;
    }
}

game.state.add('scyla', scyla);
game.state.start('scyla');

我尝试过类似的事情

let self = this

无论如何，这都会返回 windows 对象。这个和闭包有关系，但是不太明白

不知道如何解决这个问题:/

Answer 1

箭头函数将 this 设置为词法范围。您正在尝试访问 scyla 对象，但箭头函数将其设置为 window (或任何 this 等于当时的值)你声明了scyla)。

直接引用scyla:

scyla.rsGame();

或者使用标准函数表达式编写您的方法:

update: function() {
    ...
    if (this.player.inWorld === false)
        this.rsGame(); 
}

或简写方法声明:

update() {
    ...
    if (this.player.inWorld === false)
        this.rsGame();
}