排他思想：首先排除其他，然后再设置自己的样式
实例：五个按钮，点击某个按钮，其背景颜色变为粉色，其他按钮颜色默认
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<button>按钮1</button>
<button>按钮2</button>
<button>按钮3</button>
<button>按钮4</button>
<button>按钮5</button>
<script>
var btns = document.getElementsByTagName('button');
for(var i = 0;i < btns.length ; i++){
btns[i].onclick = function(){
for(var j = 0; j< btns.length;j++){
btns[j].style.backgroundColor = '';
}
this.style.backgroundColor = 'pink';
}
}
</script>
</body>
</html>