我是javascript新手,可以从下面的代码中看出来。我想为页面上的6个按钮创建事件处理程序。单击按钮后,按钮下方的代码块的显示属性将从“无”更改为“块”。为此,我需要将每个按钮与html的单个部分关联(在这种情况下,具有唯一ID的标签-pt1,pt2等)。
我为此苦了一段时间,并得到了下面的代码。那就是问题!事实证明,我要这样做完全是错误的。但是,作为一个新手,当它起作用时,我认为我正在做某事。当我花了几个小时在做这些事情时,我需要知道为什么下面的代码起作用了(这样我就会觉得自己学到了东西)。我将重点介绍代码的一部分,因为我一生都无法锻炼代码的工作原理。
var buttons = document.getElementsByClassName("CSS");
for (var i = 0; i < buttons.length; i++) {
// Generate strings associated with the button ids and the event handlers for each button
var buttonID = "button" + i;
var clickHandlerID = "clickHandler" + i;
var buttonEH = document.getElementById(buttonID);
// Identify the button elements by id
// As clickHandlerID is a string, to get the browser to recognise it as a function name
var clickHandler = window[clickHandlerID];
buttonEH.addEventListener("click", clickHandler, false);
}
/*****************************************************************************/
// Why does this work?
// clickHandler1, clickHandler2, etc are not referenced in my event handler.
// My botched attempt to create them in the event handler (var clickHandler = window[clickHandlerID];)
// resulted in "undefined" values (from console.log(clickHandler)).
// Yet it worked?!?! (I did eventually find the correct approach, a simple 10 line solution,
// but I am troubled that I don't understand what is going on here. Any help would be greatly appreciated!!)
/*****************************************************************************/
function clickHandler1 () {
if (pt1.style.display === "block") {
pt1.style.display = "none";
} else {
pt1.style.display = "block";
}
}
function clickHandler2 () {
if (pt2.style.display === "block") {
pt2.style.display = "none";
} else {
pt2.style.display = "block";
}
}
最佳答案
var buttons = document.getElementsByClassName("CSS");
for (var i = 0; i < buttons.length; i++) {
// Generate strings associated with the button ids and the event handlers for each button
var buttonID = "button" + i;
var clickHandlerID = "clickHandler" + i;
var buttonEH = document.getElementById(buttonID);
// Identify the button elements by id
// As clickHandlerID is a string, to get the browser to recognise it as a function name
var clickHandler = window[clickHandlerID];
console.log(clickHandler);
buttonEH.addEventListener("click", clickHandler, false);
}
/*****************************************************************************/
// Why does this work?
// clickHandler1, clickHandler2, etc are not referenced in my event handler.
// My botched attempt to create them in the event handler (var clickHandler = window[clickHandlerID];)
// resulted in "undefined" values (from console.log(clickHandler)).
// Yet it worked?!?! (I did eventually find the correct approach, a simple 10 line solution,
// but I am troubled that I don't understand what is going on here. Any help would be greatly appreciated!!)
/*****************************************************************************/
function clickHandler0 () {
if (pt0.style.display === "block") {
pt0.style.display = "none";
} else {
pt0.style.display = "block";
}
}
function clickHandler1 () {
if (pt1.style.display === "block") {
pt1.style.display = "none";
} else {
pt1.style.display = "block";
}
}
function clickHandler2 () {
if (pt2.style.display === "block") {
pt2.style.display = "none";
} else {
pt2.style.display = "block";
}
}
#pt0, #pt1, #pt2, #pt3 {
display: none;
}
<button id="button0" class="CSS">button 1</button>
<button id="button1" class="CSS">button 2</button>
<button id="button2" class="CSS">button 3</button>
<div id="pt0">PT1</div>
<div id="pt1">PT2</div>
<div id="pt2">PT3</div>
在顶级范围定义的所有函数和变量都将成为
window
对象的属性。因此window['clickHandler1']
等同于clickHandler1
。您的代码可以:var clickhandler = window[clickHandlerID];
当
clickHandlerID
设置为"clickHandler1"
,"clickHandler2"
等字符串时。