JavaScript function declarations and function expressions

There are two ways to define the JS function, 1, function declaration 2, function expression

The difference between the two methods is: 1, the function declaration can be called after the definition (JavaScript engine in the interpretation of all function declarations will be promoted) 2, the function expression must be defined before use. See below for an example of visual difference

function declaration

MyCount (); // correct, you can first call // definition, function declaration function MyCount () {    console.log ("Hello js");} MyCount (); // correct, can be called after

function expression

MyCount (); // error, prompt not defined // function Expression var mycount=function  () {    console.log ("Hello js");} MyCount (); // must be written after the definition

JavaScript function declarations and function expressions