[英]How to distinct the "undefined" from typeof from the undefined value itself?
这是原始代码...
if (typeof esmGrpNo != "undefined" && esmGrpNo != "" && esmGrpNo != null) {
// ...
}
我尝试并将其更改为...
if (typeof esmGrpNo != undefined && esmGrpNo != "" && esmGrpNo != null) {
// ...
}
...这也有效。 这是为什么？
使JS对象从typeof =“ object”变为typeof =“ undefined”
[英]Make a JS object go from typeof=“object” to typeof=“undefined”
什么是类型的ClojureScript模拟...来自JavaScript的未定义？
[英]What is the ClojureScript analogue of typeof … undefined from JavaScript?
typeof a =='undefined'vs typeof a ==='undefined'
[英]typeof a == 'undefined' vs typeof a === 'undefined'
级联对象声明从第二个对象开始提供未定义的typeof
[英]Cascading object declaration gives undefined typeof from second object on
置于条件中时，typeof body 从 string 变为 undefined
[英]typeof body changes from string to undefined when placed in a conditional
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