This question already has an answer here: event.preventDefault() vs. return false 11 answers Short answer, from http://api.jquery.com/event.preventdefault/ Description: If this method is called, the default action of the event will not be triggered. Take this example: $("a").click(function( event ) { event.preventDefault(); $("<div>") .append( "default " + event.type + " pr
这个问题在这里已经有了答案： event.preventDefault（）与返回false 11个答案 简短的回答，从http://api.jquery.com/event.preventdefault/ 说明：如果调用此方法，则不会触发事件的默认操作。 以这个例子： $("a").click(function( event ) { event.preventDefault(); $("<div>") .append( "default " + event.type + " prevented" ) .appendTo( "#log" ); }); 如果上面的超链接被点击，则浏览器
Possible Duplicate: event.preventDefault() vs. return false I'm not sure, but as far as I see, event.preventDefault is coming from jQuery . if yes, I'm wondering is there any native equivalent in Javascript doing the same? preventDefault is a DOM method. See the W3C specification here. jQuery wrap around native JavaScript event object. preventDefault is JavaScript method. you
可能重复： event.preventDefault（）与返回false 我不确定，但据我所知， event.preventDefault来自jQuery 。 如果是的话，我想知道Javascript中是否有任何本地等价的操作？ preventDefault是一种DOM方法。 请参阅此处的W3C规范。 jQuery环绕本地JavaScript事件对象。 preventDefault是JavaScript方法。 你可以通过return false;来实现jQuery中的preventDefault return false; 。 在jQuery事件处理程序中return
I'm trying to use Lodash to merge object A into object B, but the trouble I am having is that object A has some undefined values and I want these to be copied over to object B. Lodash docs for _.merge() says: "Recursively merges own enumerable properties of the source object(s), that don't resolve to undefined into the destination object." Is there another function that ca
我试图用Lodash把对象A合并到对象B中，但是我遇到的麻烦是对象A有一些未定义的值，我希望这些被复制到对象B. Lodash文档为_.merge（）说： “将源对象的自身可枚举属性递归合并，不解析为未定义的目标对象。” 是否有另一个功能可以做到这一点，还是可以轻易覆盖？ 编辑A： 示例输入： A = { name: "Bob Smith", job: "Racing Driver", address: undefined } B = { name: "Bob Smith", job: "Web Developer",
I am not asking if the variable is undefined or if it is null . I want to check if the variable exists or not. Is this possible? The typeof techniques don't work because they don't distinguish between when a variable has not been declared at all and when a variable has been declared but not assigned a value, or declared and set equal to undefined. But if you try to use a variable th
我不问，如果变量是未定义的或者它是否为null 。 我想检查变量是否存在。 这可能吗？ typeof技术不起作用，因为它们不区分什么时候变量尚未被声明，何时变量已被声明但未被赋值，或被声明并被设置为未定义。 但是，如果您尝试使用未在if条件中声明的变量（或在赋值的右侧），则会发生错误。 所以这应该工作： var exists = true; try { if (someVar) exists = true; } catch(e) { exists = false; } if (exis
Possible Duplicate: Detecting an undefined object property in JavaScript From the below javascript sample try { if(jsVar) { proceed(); } }catch(e){ alert(e); } this jsVar is declared and initialed in another js fine. The problem is that code throws undefined error when this code is executed before the other file (where its declared and initiated) is executed. That
可能重复： 在JavaScript中检测未定义的对象属性 从下面的JavaScript示例 try { if(jsVar) { proceed(); } }catch(e){ alert(e); } 这个jsVar被宣布并在另一个js罚款。 问题是当代码在其他文件（其声明和启动的位置）执行之前执行时，代码会抛出未定义的错误。 这就是为什么它被尝试和捕获包围。 处理这个未定义错误的最佳方式是什么？ 你可以检查事实if (typeof(jsVar) == 'undefined') {
Can I write the 'if else' shorthand without the else? eg: var x=1; x==2? dosomething:doNothingButContinueCode; I've noticed putting 'null' for the else works but I have no idea why or if that's a good idea. EDIT: Some of you seem bemused why I'd bother trying this. Rest assured it's purely out of curiosity. I like messing around with js. This is also
我可以在没有其他人的情况下写下'if else'吗？ 例如： var x=1; x==2? dosomething:doNothingButContinueCode; 我注意到为其他作品添加'null'，但我不知道为什么或者如果这是一个好主意。 编辑：你们中的一些人似乎困惑，为什么我会打扰这件事。 放心吧，这纯粹是出于好奇。 我喜欢和js混战。 这也是一个选择： x == 2 && dosomething(); dosomething()只会在x == 2被调用。 这被称为
This question already has an answer here: Difference between == and === in JavaScript [duplicate] 2 answers You need to use == or === for equality checking. = is the assignment operator. You can read about assignment operators here on MDN. I assume you know that = is for assignment, after all, you are using assignment already in the first line: var testTest = function(answer) { and I d
这个问题在这里已经有了答案： 在JavaScript和=== ===之间的差异[复制] 2个答案 您需要使用==或===进行相等性检查。 =是赋值运算符。 你可以在这里阅读有关MDN的赋值运算符。 我假设你知道=是用于赋值的，毕竟你在第一行中已经使用赋值了： var testTest = function(answer) { 我认为你认为这不会在这里比较任何东西（或者是你？）。 问题仍然存在，为什么= in if (answer = "doggies") “not work”？
This question already has an answer here: Difference between == and === in JavaScript [duplicate] 2 answers The difference between == and === is that the first one (double equals) does type coercion, which can lead to goofy results: 0 == false true 0 === false false It is usually recommended to use === as that will provide more predictable results and evaluate the true types of the values
这个问题在这里已经有了答案： 在JavaScript和=== ===之间的差异[复制] 2个答案 ==和===之间的区别是第一个（double等于）类型的强制，这可能导致愚蠢的结果： 0 == false true 0 === false false 通常建议使用===因为这将提供更多可预测的结果并评估您正在比较的值的真实类型。
This question already has an answer here: Difference between == and === in JavaScript [duplicate] 2 answers The first case is equivalent. The === performs the same operation as the == , except that it does not perform any type conversions . See this answer for more details. So, if ( variable === true || variable === false) { ... } Will evaluate to true only when variable is a boolea
这个问题在这里已经有了答案： 在JavaScript和=== ===之间的差异[复制] 2个答案 第一种情况是相同的。 ===执行与==相同的操作，只是它不执行任何类型转换 。 看到这个答案更多细节。 所以， if ( variable === true || variable === false) { ... } 只有当variable是布尔变量时才会评估为真。 至于typeof的内部工作方式，您可以阅读这些内容，当然这是手册。 请记住， typeof是一种语言运算符，很像=== ， ==或
This question already has an answer here: Which equals operator (== vs ===) should be used in JavaScript comparisons? 50 answers Difference between == and === in JavaScript [duplicate] 2 answers If the output of console.log(response) is {"type":"success","desc":"something"} then response is most likely still a string (containing JSON), and strings don't have a type property: > "f
这个问题在这里已经有了答案： 应该在JavaScript比较中使用哪个等于运算符（== vs ===）？ 50个答案 在JavaScript和=== ===之间的差异[复制] 2个答案 如果console.log(response)的输出是 {"type":"success","desc":"something"} 那么response很可能仍然是一个字符串（包含JSON），并且字符串没有type属性： > "foo".type == "error" // `undefined` is never equal to a string false 对象在控制台中通常看起来不