<!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. Why do we need logical operations?
2.What is the relationship between this.index and op.style.cssText? Can you briefly explain it?
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
That sentence means: If the button clicked is "Reset", then the
cssTextof thep1element will be cleared. That is, the initial state of thep1element is reset (without thestylevalue).&&Operations are performed from left to right, and the expression on the right is executed only when the expression on the left is true. Here, whenthis.index == oBtn.length - 1, that is, when the last button is clicked, executeop.style.cssText = "".This kind of writing is not worth promoting. It has poor readability and is not a good way of writing. The normal way to write it is:
this.indexsaves the serial number of the button and is used to determine which button was clicked. It cannot be expressed directly withi. This is a famous flaw in JavaScript.means: if it is the last btn, execute the following code
(op.style.cssText = ""), that is, clear the styleEquivalent to
if(a==b){code....}Personally I don’t like this way of writing.
this.index is the serial number of the button
op.style.cssText = ""means clearing the op style.