The const keyword of ES6 declares variables

const The keyword is used to declare constants ,const The statement has the following characteristics

1. The declaration must be assigned an initial value

2. According to habit questions Identifiers are usually uppercase

3. Duplicate statements are not allowed

4. Value cannot be modified

5. Block level scope ( local variable )

Code block example ：

The declaration must be assigned an initial value

  //  What statement must be given an initial value 
    const Sun;
    //  Running results :Uncaught SyntaxError: Missing initializer in const declaration

Duplicate statements are not allowed

   	const Animal =  ' The rabbit '
    const Animal =  ' The rabbit '
    //  Running results :Uncaught SyntaxError: Identifier 'Animal' has already been declared

Value cannot be modified （ Modification of array elements and internal modification of objects are allowed ( Arrays and objects store reference addresses ）

 	const Animal = " The rabbit "
    Animal = " Little rabbit "
    console.log(Animal);
    //  Report errors : TypeError: Assignment to constant variable

Block level scope

	 {
    
	    const Animal = " The rabbit "
	     console.log(Animal);
	     //  Print the results : The rabbit 
	 }
    console.log(Animal);
    //  Report errors  Uncaught ReferenceError: Animal is not defined

notes ： Declare object types using const, Non object type declaration selection let