与操作员进行可选检查怎么样？

例如：

// check mother for null or undefined and 
// then if mother exist check her children also
// this 100% sure it support and valid in JS today.
// Apart of that C# have almost the same operator using the same way
if (mother?.children) {

}
else {
 // it is null, undefined, etc...

}

这是对WebWander关于检查NaN的解决方案的评论（我还没有足够的代表留下正式评论）。解决方案如下

if(!parseInt(variable) && variable != 0 && typeof variable === "number")

但对于将舍入为0的有理数（例如变量=0.1），这将失败。更好的测试是：

if(isNaN(variable) && typeof variable === "number")

你可以使用try-catch finally

 try {
     document.getElementById("mydiv").innerHTML = 'Success' //assuming "mydiv" is undefined
 } catch (e) {

     if (e.name.toString() == "TypeError") //evals to true in this case
     //do something

 } finally {}   

您也可以抛出自己的错误。看看这个。

“Object.is（）”方法可用于确定两个值是否相同。因此，您可以使用它来检查对象是否为空。

检查空值

let testA = null; //null
console.log(Object.is(testA, null)); //true //null === null

if(Object.is(testA, null)) {
  console.log("This is a Null Value");
}

Output:
true
This is a Null Value

检查未定义的值

let testB; //undefined
console.log(Object.is(testB, undefined)); //true //undefined === undefined

if(Object.is(testB, undefined)) {
  console.log("This is an undefined Value");
}

Output:
true
This is an undefined Value

如果要同时检查undefined和null，请使用此选项。

let testC; //undefined
console.log(Object.is(testC, undefined)); //true //undefined === undefined
console.log(Object.is(testC, null)); //false //undefined === null

if (Object.is(testC, undefined) || Object.is(testC, null)){
  console.log("The value is either undefined or null");
}

if (!(Object.is(testC, undefined) || Object.is(testC, null))){
  console.log("The value is neither undefined nor null");
}

Output:
true
false
The value is either undefined or null

看看他们：https://onecompiler.com/javascript/3ymdqd34v

Mozilla解释：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is

通过显式检查null但使用简化的语法来改进已接受的答案：

if ([pass, cpass, email, cemail, user].every(x=>x!==null)) {
    // your code here ...
}

//测试let pass=1，cpass=1，email=1，cemail=1，user=1；//只是为了测试if（[pass，cpass，email，cemail，user].every（x=>x！==null））{//你的代码在这里。。。console.log（“Yayy！它们都不是空的”）；}其他{console.log（“哎呀！至少其中一个为空”）；}

如果布尔值来自DB，这将不起作用例如：

 value = false

 if(!value) {
   // it will change all false values to not available
   return "not available"
 }