On the difference between Const, VAR and let in JavaScript _javascript skills

Source: Internet
Author: User
Tags modifier

There are three kinds of ways to declare variables in javascript: VAR, let, Const. The following gives you a description of the three types of JS definition variables const, VAR, let the difference.

1.const-defined variables cannot be modified and must be initialized .

Const B = 2;//correct
//const b;//error, must initialize 
console.log (' Outside const definition B: ' + B ');//have output value
//b = 5;
Console.log (' Outside of the function modifier const definition B: ' + B ');//cannot be output

2.var defined variables can be modified, if not initialized will output undefined, will not error.

var a = 1;
var a;//does not error
console.log (' var definition a: ' + a ');//can output a=1
function change () {
a = 4;
Console.log (' var definition a: ' + a ' in function);//Can output a=4
} change 
();
Console.log (' var definition A is the function internal modifier value: ' + a ');//Can output a=4

3.let is a block-level scope, which has no effect on the outside function after using let definition inside the function.

Let C = 3;
Console.log (' function outside let definition C: ' + C ');/output c=3
function change () {let
c = 6;
Console.log (' function let definition C: ' + C ');//Output c=6
} change 
()
; Console.log (' function call after let definition C is not affected by function internal definition: ' + C ');//Output c=3

The above is a small set of JavaScript to introduce the Const, VAR and let the difference analysis, hope to help everyone, if you have any questions please give me a message, small series will promptly reply to everyone. Here also thank you very much for the cloud Habitat Community website support!

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