Name of the named function expression and the name of the function declaration

1 vars = 0,2b = 0;3 functionA (s) {4A =function () {5Console.log (S + b++);6     };7 Console.log (A);8Console.log (s++);9 }TenA (1); OneA (2); AConsole.log (DeleteA); -A (2);

A as a property of a global object, the value is a reference to a function, when a function is executed, an anonymous function is passed to a, then a scope chain lookup is made, a is found in the global object, and then assigned to it. Because a is a function declaration, it cannot be deleted. If you change it to the following:

1 vars = 0,2b = 0;3 functionA (s) {4D =function () {5Console.log (S + b++);6     };7 Console.log (d);8Console.log (s++);9 }TenA (1); OneD (2); AConsole.log (DeleteD);//true -D (2);

Note that D is not a variable, but is added to the global object as a property, the variable cannot be deleted, and the property can be deleted.

1 functionA () {2     functionB () {3         functionC () {4A =function () {5Console.log (1);6             };7         }8 C ();9     }Ten B (); One } A A (); -A ();//1

function declarations and function "true" names of named function expressions are different. In the above example, a is a function declaration that exists as a property of a global object and executes an assignment statement that is a in the global object that is found through the scope chain.

1(functionA () {2     functionB () {3         functionC () {4A =function () {5Console.log (1);6             };7         }8 C ();9     }Ten B (); One })(); AA ();//referenceerror:a is not defined

The name of the named function expression exists in a special object, which is between the parent scope and the A function scope, in the above example, the equivalent of adding a special object between the global object and the active object of a function, the special object has only one property that is a, the value is a function. This is why accessing the A property in a global object does not exist, only within the scope of the a function to access the A property. Other words:

1 function A () {}

1 (function A () {}) ();

The first of the above is a property that exists in the global object, and the second above is a special object that exists between a global object and the active object of a.

1 function A () {2     var A = 2; 3     Console.log (A); 4 }5 A (); // 2 6 A (); // 2

So, a variable or function with the same name as the function can be declared in the body of the function . It's just not recommended, although the syntax is correct.

1 function A () {2     function A () {3         console.log (2); 4     }5    A (); 6 }7 A (); // 2 8 A (); // 2

Name of the named function expression and the name of the function declaration