1.canvas图片预加载及进度条的实现
/*star
*loading模块
*实现图片的预加载，并显示进度条
*参数：图片数组对象，加载完成的回调函数
*/
function loadImages(sources,callback){
var loadedImages = 0;
var numImages = 0;
ctx.font='14px bold';
ctx.lineWidth=5;
var clearWidth=canvas.width;
var clearHeight=canvas.height;
// get num of sources
for (var src in sources) {
numImages++;
}
for (var src in sources) {
images[src] = new Image();
//当一张图片加载完成时执行
images[src].onload = function(){
//重绘一个进度条
ctx.clearRect(0,0,clearWidth,clearHeight);
ctx.fillText('Loading:'+loadedImages+'/'+numImages,200,280);
ctx.save();
ctx.strokeStyle='#555';
ctx.beginPath();
ctx.moveTo(200,300);
ctx.lineTo(600,300);
ctx.stroke();
ctx.beginPath();
ctx.restore();
ctx.moveTo(200,300);
ctx.lineTo(loadedImages/numImages*400+200,300);
ctx.stroke();
//当所有图片加载完成时，执行回调函数callback
if (++loadedImages >= numImages) {
callback();
}
};
//把sources中的图片信息导入images数组
images[src].src = sources[src];
}
}
//定义预加载图片数组对象，执行loading模块
window.onload = function(){
var sources = {
PaperBoy1: "images/run/PaperBoy1.png",
PaperBoy2: "images/run/PaperBoy2.png",
PaperBoy3: "images/run/PaperBoy3.png",
PaperBoy4: "images/run/PaperBoy4.png",
PaperBoy5: "images/run/PaperBoy5.png",
PaperBoy6: "images/run/PaperBoy6.png",
PaperBoy7: "images/run/PaperBoy7.png",
PaperBoy8: "images/run/PaperBoy8.png",
PaperBoy9: "images/run/PaperBoy9.png",
PaperBoy10: "images/run/PaperBoy10.png",
PaperBoy11: "images/run/PaperBoy11.png",
PaperBoy12: "images/run/PaperBoy12.png",
PaperBoy13: "images/run/PaperBoy13.png",
PaperBoy14: "images/run/PaperBoy14.png",
PaperBoy15: "images/run/PaperBoy15.png",
PaperBoy16: "images/run/PaperBoy16.png",
PaperBoy17: "images/run/PaperBoy17.png",
PaperBoy18: "images/run/PaperBoy18.png",
PaperBoy19: "images/run/PaperBoy19.png",
PaperBoy20: "images/run/PaperBoy20.png",
PaperBoy21: "images/run/PaperBoy21.png",
PaperBoy22: "images/run/PaperBoy22.png",
PaperBoy23: "images/run/PaperBoy23.png",
PaperBoy24: "images/run/PaperBoy24.png",
_Street:'images/_Street.png',
AD:'images/AD.png',
building:'images/building.png',
cloud:'images/cloud.png'
};
//执行图片预加载，加载完成后执行main
loadImages(sources,main);
};
/*end*/2.JS实现跨浏览器添加事件与移除事件怎样做才最优？
一般的兼容做法，如下：
跨浏览器添加事件
//跨浏览器添加事件
function addEvent(obj,type,fn){
if(obj.addEventListener){
obj.addEventListener(type,fn,false);
}else if(obj.attachEvent){//IE
obj.attchEvent('on'+type,fn);
}
}跨浏览器移除事件
//跨浏览器移除事件
function removeEvent(obj,type,fn){
if(obj.removeEventListener){
obj.removeEventListener(type,fn,false);
}else if(obj.detachEvent){//兼容IE
obj.detachEvent('on'+type,fn);
}
}推荐写法
function addEvent( obj, type, fn ) {
if ( obj.attachEvent ) {
obj['e'+type+fn] = fn;
obj[type+fn] = function(){obj['e'+type+fn]( window.event );}
obj.attachEvent( 'on'+type, obj[type+fn] );
} else
obj.addEventListener( type, fn, false );
}
function removeEvent( obj, type, fn ) {
if ( obj.detachEvent ) {
obj.detachEvent( 'on'+type, obj[type+fn] );
obj[type+fn] = null;
} else
obj.removeEventListener( type, fn, false );
}参考地址
addEvent() recoding contest entry
addEvent() – Follow Up
3.Ajax用jsonp方式跨域发送请求小实例
众所周知，Ajax是通过创建XMLHttpRequest对象或ActiveXObject来连接服务器、发送请求以及响应数据，但它却不能跨域。而在分布式系统中我们又需要跨域发送接受数据，于是jsonp出现了...
它是一种跨域请求方式，主要利用了script标签里的src属性，该属性可以跨域发送请求，然后服务器返回js代码，网页端便响应其信息，然后我们可以对其传过来的js代码做处理提取其中的信息。
jsonp发送请求只需在src后面添加“？callback=函数名”就可以，例如“http://www.item.com/list?callback=myfunction",则只需在服务端接受参数myfunction并将函数名与想要返回的数据拼接就可以例如在java中响应该请求，可以获取参数callback的值myfunction，再拼接成myfunction+"("+data+")"格式返回就行，在前端写同名函数接受data并处理就可以了。但在jquery中对jsonp进行了封装，返回函数就是success，数据也用success接受。
例如：
前端代码：
//发送请求
$.ajax({
//url:"http://localhost:8081/rest/itemcat/list?callback=getMessage",
url:"http://localhost:8081/rest/itemcat/message",
type:"get",
cache:false,
dataType:"jsonp",
jsonp:"callback", //这里定义了callback的参数名称，以便服务获取callback的函数名即getMessage
jsonpCallback:"getMessage", //这里定义了jsonp的回调函数
success:function(data){
alert("success:"+data);
},
error:function(){
alert("发生异常");
}
});
function getMessage(jsonp){
alert("message:"+jsonp);
}这样发出的请求为：http://localhost:8081/rest/itemcat/message?callback=getMessage
jsonp:"callback",
jsonpCallback:"getMessage",
这两个参数的值会自动拼接在url后面，所以用jquery的$.ajax方法发出的url可以不用在后面添加callback=getMessag,返回函数则变为了success而不是getMessage
4.使用高德地图API创建地图以及获取当前地址经纬度
创建API地图带有点标记
<script src="http://webapi.amap.com/maps?v=1.4.1&key=bcf87f3263f98cc37309298bca20c622"></script>
<script type="text/javascript">
// 实例化点标记
function addMarker() {
marker = new AMap.Marker({
icon: "http://webapi.amap.com/theme/v1.3/markers/n/mark_b.png",
position: [116.41, 39.91]
});
marker.setMap(map);
}
var map = new AMap.Map('container', {
resizeEnable: true,
center: [116.40, 39.91],
zoom: 13
});
addMarker();
</script>根据浏览器定位获取当前经纬度
<div id="container_display"></div>
<script src="https://webapi.amap.com/maps?v=1.4.1&key=bcf87f3263f98cc37309298bca20c622"></script>
<script>
function loadingCurrentPosition(callback){
document.getElementById('container_display').innerHTML = '';
//加载地图，调用浏览器定位服务
map = new AMap.Map('container_display', {
resizeEnable: true
});
map.plugin('AMap.Geolocation', function() {
geolocation = new AMap.Geolocation({
enableHighAccuracy: true,//是否使用高精度定位，默认:true
timeout: 10000, //超过10秒后停止定位，默认：无穷大
buttonOffset: new AMap.Pixel(10, 20),//定位按钮与设置的停靠位置的偏移量，默认：Pixel(10, 20)
zoomToAccuracy: true, //定位成功后调整地图视野范围使定位位置及精度范围视野内可见，默认：false
buttonPosition:'RB'
});
map.addControl(geolocation);
geolocation.getCurrentPosition();
AMap.event.addListener(geolocation, 'complete', onComplete);//返回定位信息
AMap.event.addListener(geolocation, 'error', onError); //返回定位出错信息
});
//解析定位结果
function onComplete(data) {
var getLngdata = data.position.getLng();
var getLatdata = data.position.getLat();
if(callback){
callback(getLngdata,getLatdata); //回调参数中传递经度与纬度
}
}
//解析定位错误信息
function onError(data) {
alert('定位失败');
}
}
$(function(){
var getLng = ''; //存经度
var getLat = ''; //存纬度
//默认加载一次自动获取当前人的位置
loadingCurrentPosition(function(lngdata,Latdata){
getLng = lngdata;
getLat = Latdata;
});
$(".getCurrentPosition").on('click',function(){
loadingCurrentPosition(function(lngdata,Latdata){
getLng = lngdata;
getLat = Latdata;
});
});
})
</script>高德地图根据浏览器定位获取当前经纬度API案例地址：http://lbs.amap.com/api/javascript-api/example/location/browser-location
高德开放平台：http://lbs.amap.com/api
5.JS创建canvas学习小例代码
1.HTML5中的Canvas标签的创建
window.onload = function(){
createCanvas();
}
function createCanvas(){
var canvas_width= 200, canvas_height = 200;
document.body.innerHTML = "<canvas id=\"canvas\" width=\""+canvas_width+"\" height=\""+canvas_height+"\"></canvas>";
}2.HTML5Canvas标签绘制图形
var canvas_width= 500, canvas_height = 500;
var mycanvas, context;
window.onload = function(){
createCanvas();
drawRect();
}
function createCanvas(){
document.body.innerHTML = "<canvas id=\"mycanvas\" width=\""+canvas_width+"\" height=\""+canvas_height+"\"></canvas>";
mycanvas = document.getElementById("mycanvas");
context = mycanvas.getContext("2d");
}
function drawRect(){
context.fillStyle ="#FF0000";
//context.rotate(45);//旋转45度
//context.translate(200,200);//移动
//context.scale(2,0.5);//缩放
context.fillRect(0,0,200,200);
}3.HTML5Canvas标签绘制图片
var canvas_width= 500, canvas_height = 500;
var mycanvas, context;
window.onload = function(){
createCanvas();
drawImage();
}
function createCanvas(){
document.body.innerHTML = "<canvas id=\"mycanvas\" width=\""+canvas_width+"\" height=\""+canvas_height+"\"></canvas>";
mycanvas = document.getElementById("mycanvas");
context = mycanvas.getContext("2d");
}
function drawImage(){
var img = new Image();
img.onload = function(){
context.drawImage(img,0,0);
}
img.src = "1.png";
}
html5
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