javascript - js，有几行代码不太明白？
<!Doctype html>
<html lang="en>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>控制p属性</title>
<script>
var changeStyle = function(elem, attr, value) {
elem.style[attr] = value
};
window.onload = function() {
var oBtn = document.getElementsByTagName("input");
var op = document.getElementById("p1");
var oAtt = ["width", "height", "background", "display", "display"];
var oVal = ["200px", "200px", "red", "none", "block"];
for (var i = 0; i < oBtn.length; i++) {
oBtn[i].index = i;
oBtn[i].onclick = function() {
this.index == oBtn.length - 1 && (op.style.cssText = "");
changeStyle(op, oAtt[this.index], oVal[this.index])
}
}
};
</script>
</head>
<body>
<p id="outer">
<input type="button" value="变宽" />
<input type="button" value="变高" />
<input type="button" value="变色" />
<input type="button" value="隐藏" />
<input type="button" value="重置" />
<p id="p1"></p>
</p>
</body>
</html>1.为什么要逻辑运算？
2.this.index 与 op.style.cssText之间是怎么样的关系，能简单说一下吗？
