We then use "if not" (!) to check if the player has entered a valid choice. If choice is null, undefined, or an empty string, the condition inside the first if statement is true, and the code inside the block is executed. Therefore, the output to the console is "You didn't ...
if(data ===null){console.log("data中没有保存对象引用!");} null 使用 那么我们在什么情况下需要将变量赋值为null呢?这里我想到的有两种情况。 如果定义的变量在将来用于保存对象,那么最好将该变量初始化为null,而不是其他值。换句话说,只要意在保存对象的变量...
function(){if(document.readyState==="complete"){init();}}); 代码语言:javascript 代码运行次数:0 运行 AI代码解释 location~^/assets/{add_header Access-
Repeat,whilematchSucceeded isfalseIf i<0ori>length,thenCall the [[Put]]internalmethodofRwitharguments "lastIndex", 0,andtrue. Returnnull. Call the [[Match]]internalmethodofRwitharguments Sandi. If [[Match]] returned failure,thenLet i=i+1.elseLet r be the State resultofthe callto[[Match]...
functioninit(){varmyButton=document.getElementById("myButton");varmyTextfield=document.getElementById("myTextfield");myButton.onclick=function(){varuserName=myTextfield.value;}}document.addEventListener('readystatechange',function(){if(document.readyState==="complete"){init();}}); 4. (unknown...
If x is NaN, return false. If y is NaN, return false. If x is the same number value as y, return true. If x is +0 and y is -0, return true. If x is -0 and y is +0, return true. Return false. If Type(x) is String, then return true if x and y are exactly the ...
null表示一个空值或者被明确赋值为null的对象。它是一个表示空或不存在对象的特殊值。 简单来说,undefined表示缺少预期的值,而null表示没有值。 5. 什么是原始类型和引用类型? 在JavaScript中,数据类型分为原始类型和引用类型。 原始类型是指存储简单数据值的数据类型,包括以下五种: ...
If no tab was already active, then the hide.bs.tab and hidden.bs.tab events will not be fired. Event TypeDescription show.bs.tab This event fires on tab show, but before the new tab has been shown. Use event.target and event.relatedTarget to target the active tab and the previous act...
map(num => { if (typeof num === "number") return; return num * 2; }); A: [] B: [null, null, null] C: [undefined, undefined, undefined] D: [ 3 x empty ] 答案: C 对数组进行映射的时候,num就是当前循环到的元素. 在这个例子中,所有的映射都是number类型,所以if中的判断typeof...
But what if we were to do this: deletesecondObj.name; We’d then get: console.log(secondObj.name);// -> Results in 'undefined' But wouldn’t it be nicer for this to revert to ‘default’? This can easily be done if we modify the original code to leverage prototypal inheritance, ...