Scope of the JS variable

The difference between a 1.js function declaration and a function expression

the function declaration in JS refers to the following form:

function A () {}

The function expression in JS refers to the following form:

var a=function () {}

The parser of JS does not treat function declaration and function expression equally.

For a function declaration, theJS parser takes precedence over the read, ensuring that the declaration has been parsed before all code executes, and that the function expression, like a variable of other primitive types, is parsed only when it executes to a sentence .

So in practice, they will be different, specifically, when using the form of a function declaration to define a function, you can call the method after the function declaration, the latter, this will be an error.

Scope of the JS variable