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[英]how can the HTML in my IDE and HTML in chrome dev tools when inspected differ
[英]Why an assigned variable in JS is undefined when inspected in dev tools?
為什么在開發工具中檢查JS中的賦值變量時未定義?
例如,
var x = 5;
在devtools中導致未定義。
控制台不會評估x的值,但會評估表達式本身,表達式始終在javascript中未定義。
示例1 =>
var x = 55; // undefined
它聲明變量x並為其分配undefined值。 這就是我們在控制台上獲得的反饋值。
然后,它最終將值55分配給x。 此時控制台已經返回了一個值,因此當我們一次聲明並分配一個變量時,我們不會看到值55作為反饋。
另一方面,如果稍后將變量x重新分配給其他值,我們將獲得新值作為反饋,而不是未定義:
示例2 =>
x = 57; //57
We are declaring a variable but of which type it does not define (like string, int, or boolean) that's why it displays undefined as a first statement. after it assigns a value to a variable and decides the type of variable in Javascript.
like var a=10; // undefined as first time when var is created.
typeof(a) // "number" in second statement
-- IN addition for the function in Javascript ---------------
(function (){return("OK")})()
(function (){})()
Undefined is about the return value of a function call.
You only see something useful when a function returns value.
If nothing is returned then you see undefined.
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