本文来做一个简单的实时获取鼠标坐标的功能，在canvas动画开发中，获取鼠标的坐标，键盘的按键等等，都是常用的操作，我们就慢慢得把他们封装成一个公共库。
一、事件的兼容：
1 functionbindEvent(obj, event, fn) {2 if (obj.attachEvent) { //ie
3 obj.attachEvent(\'on\' + event, function() {4 fn.call(obj);5 });6 } else{7 //chrome&ff
8 obj.addEventListener(event, fn, false);9 }10 }
上面兼容ie8以及修正this关键字在ie低版本的指向，下面兼容chrome和ff。其他更常用的封装可以参考我的javascript开源框架gdom
二、用立即表达式搭建一个基本的库
添加获取鼠标坐标的方法
1 ;(function(window) {2 window.G ={};3 functionbindEvent(obj, event, fn) {4 if (obj.attachEvent) { //ie
5 obj.attachEvent(\'on\' + event, function() {6 fn.call(obj);7 });8 } else{9 //chrome&ff
10 obj.addEventListener(event, fn, false);11 }12 }13
14 G.getPos = function( dom ){15 var oPos = { x : 0, y : 0};16 bindEvent( dom, \'mousemove\', function( ev ){17 var oEvent = ev ||event, x, y;18 if ( oEvent.pageX ||oEvent.pageY ){19 x =oEvent.pageX;20 y =oEvent.pageY;21 }else{22 x = oEvent.clientX + document.body.scrollLeft ||document.documentElement.scrollLeft;23 y = oEvent.clientX + document.body.scrollTop ||document.documentElement.scrollTop;24 }25 x -=dom.offsetLeft;26 y -=dom.offsetTop;27 oPos.x =x;28 oPos.y =y;29 } );30 returnoPos;31 };32
33 })(window);
三、引入封装的js库，绑定canvas为监听对象，打印当前鼠标的坐标
鼠标的坐标，我这里画了2根线，便于观察.
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3
4 ;(function(window) {5 window.G ={};6 functionbindEvent(obj, event, fn) {7 if (obj.attachEvent) { //ie
8 obj.attachEvent(\'on\' + event, function() {9 fn.call(obj);10 });11 } else{12 //chrome&ff
13 obj.addEventListener(event, fn, false);14 }15 }16
17 G.getPos = function( dom ){18 var oPos = { x : 0, y : 0};19 bindEvent( dom, \'mousemove\', function( ev ){20 var oEvent = ev ||event, x, y;21 if ( oEvent.pageX ||oEvent.pageY ){22 x =oEvent.pageX;23 y =oEvent.pageY;24 }else{25 x = oEvent.clientX + document.body.scrollLeft ||document.documentElement.scrollLeft;26 y = oEvent.clientX + document.body.scrollTop ||document.documentElement.scrollTop;27 }28 x -=dom.offsetLeft;29 y -=dom.offsetTop;30 oPos.x =x;31 oPos.y =y;32 } );33 returnoPos;34 };35
36 })(window);37
38
39 #canvas{40 border:1px dashed #aaa;41 }42
43
44 window.onload = function(){45 var oCanvas = document.querySelector( "#canvas"),46 oGc = oCanvas.getContext( \'2d\'),47 width = oCanvas.width, height =oCanvas.height,48 oInfo = document.querySelector( "#info"),49 oPos =G.getPos( oCanvas );50 oCanvas.addEventListener( "mousemove", function(){51
52 oGc.clearRect( 0, 0, width, height );53 oGc.beginPath();54 oGc.moveTo( oPos.x, 0);55 oGc.lineTo( oPos.x, height );56 oGc.moveTo( 0, oPos.y );57 oGc.lineTo( width, oPos.y );58 oGc.closePath();59 oGc.strokeStyle = \'#09f\';60 oGc.stroke();61
62 oInfo.innerHTML = \'鼠标的当前坐标是:(\' + oPos.x + \',\' + oPos.y + \')\';63 }, false);64 }65
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四、点击\'run code\'可以预览效果额
;(function (window) {
window.G = {};
function bindEvent(obj, event, fn) {
if (obj.attachEvent) { //ie
obj.attachEvent(\'on\' + event, function () {
fn.call(obj);
});
} else {
//chrome&ff
obj.addEventListener(event, fn, false);
}
}
G.getPos = function( dom ){
var oPos = { x : 0, y : 0 };
bindEvent( dom, \'mousemove\', function( ev ){
var oEvent = ev || event, x, y;
if ( oEvent.pageX || oEvent.pageY ){
x = oEvent.pageX;
y = oEvent.pageY;
}else {
x = oEvent.clientX + document.body.scrollLeft || document.documentElement.scrollLeft;
y = oEvent.clientX + document.body.scrollTop || document.documentElement.scrollTop;
}
x -= dom.offsetLeft;
y -= dom.offsetTop;
oPos.x = x;
oPos.y = y;
} );
return oPos;
};
})(window);
#canvas{
border:1px dashed #aaa;
}
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( \'2d\' ),
width = oCanvas.width, height = oCanvas.height,
oInfo = document.querySelector( "#info" ),
oPos = G.getPos( oCanvas );
oCanvas.addEventListener( "mousemove", function(){
oGc.clearRect( 0, 0, width, height );
oGc.beginPath();
oGc.moveTo( oPos.x, 0 );
oGc.lineTo( oPos.x, height );
oGc.moveTo( 0, oPos.y );
oGc.lineTo( width, oPos.y );
oGc.closePath();
oGc.strokeStyle = \'#09f\';
oGc.stroke();
oInfo.innerHTML = \'鼠标的当前坐标是:(\' + oPos.x + \',\' + oPos.y + \')\';
}, false );
}
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