解决事件绑定覆盖问题

window.onload =function(){
    alert('journey');
}

if(typeof  window.onload == 'function'){
    var saved = null;
    saved = window.onload;
}
//saved就是window.onload，saved()相当于window.onload()，但是window.onload()不能执行的所以saved()相当于window.onload = function(){}
window.onload = function(){
    saved();
    alert('Mr.journey');
}



//事件切换器
window.onload = function(){
    
    var box = document.getElementById('box');
    box.onclick = function(){
        alert('journey');
        toBlue;
    }
}

function toBlue(){
    this.className='blue';
    this.onclick=toBlue;
}

function toRed(){
    this.className='red';
    this.onclick=toRed;
}