Question

我正在努力完成一个简单的画布游戏。我收到此错误：

未捕获的TypeError：allEnemies.forEach不是函数

为什么我收到此错误？

我在下面展示了我如何宣布所有敌人。根据指示，allEnemies应该是一个对象数组。

我对所有敌人的宣告是错误的还是敌人宣称错误的对象？

这是Enemy的声明，我认为他们正在尝试声明一个对象（我从未见过像这样的对象声明）我认为这是一个IIFE正确吗？

var Enemy = function() {
    // Variables applied to each of our instances go here,
    // we've provided one for you to get started

    // The image/sprite for our enemies, this uses
    // a helper we've provided to easily load images
    this.sprite = 'images/enemy-bug.

以下是整个app.js文件：

    // Enemies our player must avoid
var Enemy = function() {
    // Variables applied to each of our instances go here,
    // we've provided one for you to get started

    // The image/sprite for our enemies, this uses
    // a helper we've provided to easily load images
    this.sprite = 'images/enemy-bug.png';
}

// Update the enemy's position, required method for game
// Parameter: dt, a time delta between ticks
Enemy.prototype.update = function(dt) {
    // You should multiply any movement by the dt parameter
    // which will ensure the game runs at the same speed for
    // all computers.
}

// Draw the enemy on the screen, required method for game
Enemy.prototype.render = function() {
    ctx.drawImage(Resources.get(this.sprite), this.x, this.y);
}

// Now write your own player class
// This class requires an update(), render() and
// a handleInput() method.
var Player = function() {
    // Variables applied to each of our instances go here,
    // we've provided one for you to get started


    this.sprite = 'images/char-pink-girl.png';
}

// Now instantiate your objects.
// Place all enemy objects in an array called allEnemies
// Place the player object in a variable called player
var allEnemies = [];
allEnemies = Enemy;

var player = Player;


// This listens for key presses and sends the keys to your
// Player.handleInput() method. You don't need to modify this.
document.addEventListener('keyup', function(e) {
    var allowedKeys = {
        37: 'left',
        38: 'up',
        39: 'right',
        40: 'down'
    };

    player.handleInput(allowedKeys[e.keyCode]);
});

这是给我错误类型的代码行：

allEnemies.forEach(function(enemy) {

这是函数声明的其余部分：

function updateEntities(dt) {
        allEnemies.forEach(function(enemy) {
            enemy.update(dt);
        });
        player.update();
    }

Answer 1

第1行allEnemies是一个数组下一行变为Enemy。

var allEnemies = [];
allEnemies = Enemy;

Enemy是一个功能 allEnemies现在是一个功能。

Function.prototype.forEach是undefined

Answer 2

问题在这里

   allEnemies = Enemy;

您将 allEnemies 声明为数组但是您使用上述语句覆盖了它。现在 allEnemies 是一个简单的函数而不是数组。因此，每个都是未定义的。

要创建一个Enemy对象数组，您应该执行以下操作：

   allEnemies.push(Enemy);

Javascript：这段代码片段的作用和错误代码Uncaught TypeError：allEnemies.forEach不是函数

2 个答案: