Js- declare variables

JS declare variables

Js way to declare variables There are three: let, const, var

1.const If the definition of simple data types, becomes constant, variable values ​​can not be changed.

const name="lili";
name="lucy";
console.log(name);//error

 

2.Var can repeat declare a variable, and covers the value of the variable, and variables defined wherever, are global variables. If the second var statement but did not assign the same variable, the variable is assigned a value, or a statement of the first value.

was test = 3 ;
was the test; 
console.log (test); // 3

was test = 3 ;
was test = 5 ; 
console.log (test); // 5

 

3.Let not repeat the statement, repeated error statement. Locally declared as local variables defined in the global, compared with global variables. Define local repeated, preferentially used locally defined variables.

let a=10;
{
    let a=12;
    console.log(a);//a=12

}
console.log(a);//a=10