Question

所以我不知道为什么，在第35行，我得到这个错误，有人可以解释为什么这不起作用，因为我似乎无法弄清楚为什么？

这是其上传的网页的链接，您可以在控制台中看到错误消息，以及所有代码。 http://matthew-hoyle.co.uk/files/beta/projects/platformer.php

window.onload = function() {
var canvas = document.getElementById("canvas");
var c = canvas.getContext("2d");

canvas.width  = 800;
canvas.height = 600;

function Player() {
    this.width = 20;
    this.height = 20;
    this.color = "red";
    this.posY = (canvas.height / 2) - (this.height / 2);
    this.posX = (canvas.width / 2) - (this.width / 2);
    this.volY = 0;
    this.volX = 0;
    this.gravity = 0.5;
    this.onGround = true;
    this.draw = function() {this.posY += this.volY;
        this.posX += this.volX;
        this.volY += this.gravity;

        c.fillStyle = this.color;
        c.fillRect(this.posX, this.posY, this.width, this.height);
    };
}

function Obstacle(x,y,w,h,c) {
    this.posY = y;
    this.posX = x;
    this.width = w;
    this.height = h;
    this.color = c;
    this.draw = function() {
        c.fillStyle = this.color;
        c.fillRect(this.posX, this.posY, this.width, this.height);
    };
}

//objects
var player = new Player();
var ground = new Obstacle(0, canvas.height-20,canvas.width,20,"red");

//game update loop
window.setInterval(function() {
    //clears screen
    c.fillStyle = "lightblue";
    c.fillRect(0,0, canvas.width, canvas.height);

    //drawing objects
    player.draw();
    ground.draw();
}, 30);

};

Answer 1

var ground = new Obstacle(0, canvas.height-20,canvas.width,20,"red");

在此您将ground初始化为Obstacle，其中包含5个参数。第五个c是字符串"red"。因此，稍后您调用ground.draw()时，您尝试调用"red".fillRect，而这不是字符串的有效成员函数。

基本问题是c构造函数的参数Obstacle隐藏了全局c变量，因为它是一个更近的范围，因此隐藏了您打算使用的画布上下文引用。

我不知道为什么我得到一个＆＃34; undefined不是一个函数＆＃34;错误

1 个答案: