I've been told not to use for...in with arrays in JavaScript. Why not? 原因是一个构造： var a = []; // Create a new empty array. a[5] = 5; // Perfectly legal JavaScript that resizes the array. for (var i = 0; i < a.length; i++) { // Iterate over numeric indexes from 0 to 5, as everyone expects. console.log(a[i]); } /* Will display: undefined undefined unde
我被告知不要在JavaScript for...in使用数组。 为什么不？ 原因是一个构造： var a = []; // Create a new empty array. a[5] = 5; // Perfectly legal JavaScript that resizes the array. for (var i = 0; i < a.length; i++) { // Iterate over numeric indexes from 0 to 5, as everyone expects. console.log(a[i]); } /* Will display: undefined undefined undefined undefined
I always assumed caching the length of an array in JavaScript is a good idea (especially in the condition of a for loop) because of the expensiveness of calculating the length of an array. Example for (var i = 0; i < arr.length; i++) { } // vs for (var i = 0, arrLength = arr.length; i < arrLength; i++) { } However, I thought perhaps the length property is only updated on creation and
由于计算数组的长度非常昂贵，我总是假设在JavaScript中缓存数组的长度是一个好主意（特别是在for循环中）。 例 for (var i = 0; i < arr.length; i++) { } // vs for (var i = 0, arrLength = arr.length; i < arrLength; i++) { } 然而，我想可能length属性只是在创建和更改数组时进行更新。 因此，阅读它不应该太昂贵的操作，而不是阅读它存储在一个变量（而不是其他语言中的其他方法，可能需要在内存中寻找的东
var var1 = 1, var2 = 1, var3 = 1; This is equivalent to this: var var1 = var2 = var3 = 1; I'm fairly certain this is the order the variables are defined: var3, var2, var1, which would be equivalent to this: var var3 = 1, var2 = var3, var1 = var2; Is there any way to confirm this in JavaScript? Using some profiler possibly? Actually, var var1 = 1, var2 = 1, var3 = 1; is not eq
var var1 = 1, var2 = 1, var3 = 1; 这相当于这样的： var var1 = var2 = var3 = 1; 我相当肯定，这是变量定义的顺序：var3，var2，var1，它等同于： var var3 = 1, var2 = var3, var1 = var2; 有什么方法可以在JavaScript中确认这一点吗？ 可能使用一些分析器？ 其实， var var1 = 1, var2 = 1, var3 = 1; 不等同于： var var1 = var2 = var3 = 1; 区别在于范围： function good() { var var1 = 1, var2
I am creating a game that randomly displays circles onto a canvas. The circles objects are added to an array and whenever the player collides with one of them I want to remove that object. Here is my code currently for the collision - for(var i = 0; i < currentGame.items.length; i++) { if (player1.x < currentGame.items[i].x + currentGame.items[i].radius*2 && play
我正在创建一个随机在画布上显示圆圈的游戏。 圆对象被添加到一个数组，每当玩家与其中一个碰撞，我想删除该对象。 这是我的代码目前的碰撞 - for(var i = 0; i < currentGame.items.length; i++) { if (player1.x < currentGame.items[i].x + currentGame.items[i].radius*2 && player1.x + currentGame.items[i].radius*2 > currentGame.items[i].x && player1
What is the difference between = , == , and === ? I think using one equal sign is to declare a variable while two equal signs is for a comparison condition and lastly three equal signs is for comparing values of declared variables. You have = the assignment operator , == the 'equal' comparison operator and === the 'identical' comparison operator . $a = $b Assign Sets
= ， ==和===之间有什么区别？ 我认为使用一个等号表示要声明一个变量，而两个等号用于比较条件，最后三个等号用于比较声明变量的值。 您有= 赋值运算符 ， == '等于'比较运算符和=== '相同'比较运算符 。 $a = $b Assign Sets $a to be equal to $b. $a == $b Equal TRUE if $a is equal to $b. $a === $b Identical TRUE if $a is equal to $b, and they are of the same type. (in
I know this is a bit of perennial question, but here goes: I want to know whether the device my site is being accessed with is a touchscreen. That means phones and iPads, of course, which are individually detectable, but also other touchscreens that may well be running flavors of Windows. Any chance of determining the presence or absence of a mouse on those? Let's say I'm willing to u
我知道这是一个长期存在的问题，但是这里有一个问题：我想知道我的网站正在访问的设备是否是触摸屏。 这意味着手机和iPad当然可以单独检测，但也有其他触摸屏可能会运行Windows的风格。 有没有机会确定这些鼠标的存在与否？ 假设我愿意使用像Modernizr这样的大型JavaScript库。 这会有帮助吗？ 你可能想看看MobileESP。 不只是触摸屏，但它至少可以提供一些检测功能。 从他们的页面： MobileESP项目旨在为网站开发人
I need to offset the time by an hour if it's currently DST in the Pacific Time Zone. How can I determine the current daylight savings status of the Pacific Time Zone, regardless of the user's local timezone? Here's what I have so far. "dst" in line 4 is just a placeholder for a function that would tell me if daylight savings time is active in that zone. function checkTi
如果当前DST在太平洋时区，我需要将时间补偿一小时。 无论用户当地的时区如何确定太平洋时区的当前夏令时状态？ 这是迄今为止我所拥有的。 第4行中的“dst”只是一个函数的占位符，它会告诉我夏令时是否在该区域中处于活动状态。 function checkTime() { var d = new Date(); var hour = d.getUTCHours(); var offset = dst ? 7 : 8; // is pacific time currently in daylight savings? // is it curr
I have <input type="checkbox" id="checkbox1" /> <br /> <input type="text" id="textbox1" /> and $(document).ready(function() { //set initial state. $('#textbox1').val($(this).is(':checked')); $('#checkbox1').change(function() { $('#textbox1').val($(this).is(':checked')); }); $('#checkbox1').click(function() { if (!$(this).is(':checked')) {
我有 <input type="checkbox" id="checkbox1" /> <br /> <input type="text" id="textbox1" /> 和 $(document).ready(function() { //set initial state. $('#textbox1').val($(this).is(':checked')); $('#checkbox1').change(function() { $('#textbox1').val($(this).is(':checked')); }); $('#checkbox1').click(function() { if (!$(this).is(':checked')) {
How can I check if a checkbox in a checkbox array is checked using the id of the checkbox array? I am using the following code, but it always returns the count of checked checkboxes regardless of id. function isCheckedById(id) { alert(id); var checked = $("input[@id=" + id + "]:checked").length; alert(checked); if (checked == 0) { return false; } else { return true; } } I
如何使用复选框数组的ID检查复选框数组中的复选框？ 我正在使用下面的代码，但它总是返回选中的复选框的计数，而不管id。 function isCheckedById(id) { alert(id); var checked = $("input[@id=" + id + "]:checked").length; alert(checked); if (checked == 0) { return false; } else { return true; } } ID在文档中必须是唯一的，这意味着您不应该这样做： <input type="checkbox" name="chk[]
Since the upgrade to iOS 6, we are seeing Safari's web view take the liberty of caching $.ajax calls. This is in the context of a PhoneGap application so it is using the Safari WebView. Our $.ajax calls are POST methods and we have cache set to false {cache:false} , but still this is happening. We tried manually adding a TimeStamp to the headers but it did not help. We did more research
自升级到iOS 6以来，我们看到Safari的Web视图冒险缓存$.ajax调用。 这是在PhoneGap应用程序的上下文中，因此它使用的是Safari WebView。 我们的$.ajax调用是POST方法，我们将缓存设置为false {cache:false} ，但仍然存在。 我们尝试手动添加TimeStamp到标题，但它没有帮助。 我们做了更多的研究，发现Safari只是返回具有静态功能签名且不会因呼叫而改变的Web服务的缓存结果。 例如，想象一个叫做如下的函数： getNewRecord