源码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
</body>
<script src='./doem1.js'></script>
</html>
window.onload = function() {
test1();
test2();
test3();
}
function test1(){
console.log('测试1');
}
function test2(){
console.log('测试2');
}
function test3(){
console.log('测试3');
}
function addLoadEvent(func) {
var oldonload = window.onload;//将现有的事件处理函数的值存入变量中
if (typeof window.onload != 'function') {
window.onload = func;//如果这个事件处理函数没有绑定任何函数，就把新函数添加给它
} else {
window.onload = function() {
oldonload();
func();//如果已经绑定了函数，就把新函数追加到现有指令的末尾
}
}
}
addLoadEvent(test1);
addLoadEvent(test2);
