我有两个文件：sim.js，simulator.html
在simulator.html中，我在sim.js代码中加载了<head>，并在<canvas> <body>中创建了simulator.html代码
但是，当我使用document.getElementsByTagName("canvas")[0]时，它会返回undefined。
在我的simulator.html：
<!doctype html>
<html lang="en" data-manifest="" data-framework="typescript">
<head>
<meta charset="utf-8">
<title>Traffic Simulator</title>
<link rel="stylesheet" type="text/css" href="/sim/sim.css">
<style>
body {
background: transparent;
overflow: hidden;
}
</style>
<script src='http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js'></script>
<!-- preload index.js
<script>
$(document).ready(function(){
$("script").attr('src','TrafficSimulation/js/index.js')
});
</script> -->
<script src="/cdn/bluebird.min.js"></script>
<script src="/cdn/pxtsim.js"></script>
<script src="/sim/sim.js"></script>
<link rel="stylesheet" href="TrafficSimulation/css/style.css">
</head>
<body>
<div id="svgcanvas" style="height: 270;">
<canvas class="vis">
<div></div>
</canvas>
<div class="box">
Number of Cars:<br>
<br><input type="range" max="100" min="10" value="36" onChange="init();">
<span class="car_no">10</span>
</div>
<script></script>
</div>
</body>
在我的sim.js：
var __extends = (this && this.__extends) || function (d, b) {
for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
function __() { this.constructor = d; }
d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
/// <reference path="../libs/core/enums.d.ts"/>
var pxsim;
(function (pxsim) {
var loops;
(function (loops) {
/**
* Repeats the code forever in the background. On each iteration, allows other code to run.
* @param body the code to repeat
*/
//% help=functions/forever weight=55 blockGap=8
//% blockId=device_forever block="forever"
function forever(body) {
pxsim.thread.forever(body);
}
loops.forever = forever;
/**
* Pause for the specified time in milliseconds
* @param ms how long to pause for, eg: 100, 200, 500, 1000, 2000
*/
//% help=functions/pause weight=54
//% block="pause (ms) %pause" blockId=device_pause
function pauseAsync(ms) {
return Promise.delay(ms);
}
loops.pauseAsync = pauseAsync;
})(loops = pxsim.loops || (pxsim.loops = {}));
})(pxsim || (pxsim = {}));
function logMsg(m) { console.log(m); }
var pxsim;
(function (pxsim) {
var console;
(function (console) {
/**
* Print out message
*/
//%
function log(msg) {
logMsg("CONSOLE: " + msg);
// why doesn't that work?
//board().writeSerial(msg + "\n")
}
console.log = log;
})(console = pxsim.console || (pxsim.console = {}));
})(pxsim || (pxsim = {}));
var pxsim;
(function (pxsim) {
var actions;
(function (actions) {
/**
* Set location of the traffic light on the map
* @param location
*/
//% blockId=set_traffic_light block="set traffic light at %location"
function setTLightLocation(location) {
if (location == 0 /* A1 */) {
pxsim.board().setTrafficLight();
}
}
actions.setTLightLocation = setTLightLocation;
})(actions = pxsim.actions || (pxsim.actions = {}));
})(pxsim || (pxsim = {}));
/// <reference path="../node_modules/pxt-core/typings/globals/bluebird/index.d.ts"/>
/// <reference path="../node_modules/pxt-core/built/pxtsim.d.ts"/>
//declaring variable from the js library
//declare let ctx: CanvasRenderingContext2D;
// declare let car_no: number;
// declare let w: number;
// declare let h: number;
// //declare let roads: any[];
// //declare let intersections_arr: any[];
// //declare let cars: any[];
// declare let drawIntersection: any;
// declare let requestAnimFrame: any;
// //declare let canvas: HTMLCanvasElement;
// //Test variables
// declare let testV:any;
// //
// declare function distance_check(c1:any, c2:any, axis: string): boolean;
// declare function check_inter(c:any, inter:any, axis:string): boolean;
// declare function gen_dir(c:any, inter:any): void;
// declare function init(): void;
// declare function drawscene(): void;
// declare function left_greenc(): void;
// declare function drive_cars(): any;
// declare function drawcar(): any;
// declare function intersections(): any;
// declare function drawroad(): any;
// declare function animloop(): any;
// //Test Functions
// declare function checkFile(): any;
// //
/**
* Code
*/
var pxsim;
(function (pxsim) {
/**
* This function gets called each time the program restarts
*/
pxsim.initCurrentRuntime = function () {
pxsim.runtime.board = new Board();
};
/**
* Gets the current 'board', eg. program state.
*/
function board() {
return pxsim.runtime.board;
}
pxsim.board = board;
/**
* Represents the entire state of the executing program.
* Do not store state anywhere else!
*/
var Board = (function (_super) {
__extends(Board, _super);
function Board() {
_super.call(this);
//this.element = <HTMLDivElement><any>document.getElementById('svgcanvas');
}
Board.prototype.initAsync = function (msg) {
document.body.innerHTML = ''; // clear children
// document.body.appendChild(this.element);
return Promise.resolve();
};
Board.prototype.setTrafficLight = function () {
// ctx.save()
// ctx.fillStyle = 'green';
// ctx.fillRect(10,10,50,50);
// ctx.fill();
// ctx.restore();
// console.log("end1");
};
return Board;
}(pxsim.BaseBoard));
pxsim.Board = Board;
var requestAnimFrame = (function () {
return window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
// window.mozRequestAnimationFrame ||
// window.oRequestAnimationFrame ||
// window.msRequestAnimationFrame ||
// window.mozRequestAnimationFrame ||
// window.oRequestAnimationFrame ||
// window.msRequestAnimationFrame ||
function (callback) {
window.setTimeout(callback, 1000 / 60);
};
})();
var car_no = 10;
var canvas = document.getElementsByTagName("canvas")[0];
var ctx = canvas.getContext("2d");
变量canvas未定义