Javascript 标识符已声明

Question

Why does the outer declaration cause an identifier error, while the inner declaration is fine?

 function outer() { function inner() { console.log('Executing inner function'); } var inner = new inner(); } var outer = new outer();

If you change the last line to var x = new outer(); , it'll run fine.

Answer 1

I believe you have found the answer yourself. In this case, there is a confusion in the language flow due to the use of the same name for the function ( function outer() ), global variable ( var outer ) and object ( new inner() ). Be more semantic with the name of the functions, variables and objects you intend to use.

Answer 2

This is because of Local and Global declarations of Variables/Objects.

1. var inner is considered as a local variable and it can have the same name .

2. var outer is declared outside of Outer Function. So it is considered as an non local variable. So it must have an unique name than the existing ones.

Answer 3

I restructured your code in a way that works with your original idea. Basically I read the MDN documentation about possible errors with the new operator. What happens is that the new operator needs a function that defines a scope so that only afterwards can it be stored in a variable and can return whatever you want. In the documentation of this part there are some examples of errors that I believe would clarify your doubts. MDN: TypeError: "x" is not a constructor

 function showTheOuterFn() { function fnInner() { console.log('Executing inner function'); } let getInner = new fnInner(); } let outer = new showTheOuterFn();