javascript numbers- immutable

Question

I come from c# background where immutable is achieved with public get ,private set properties. I have read that numbers in javascript are immutable so how can I do the following

var x = 6 / 2;
console.log(x);  // 3
 x = 8;
console.log(x); // 8

I have changed x, which I thought I couldn't?

Answer 1

The numbers themselves are immutable. The references to them that are stored in the variable are not.

So 6 / 2 gets you a reference to the immutable 3, and then = 8 assigns a new reference to the immutable 8.

Answer 2

C# also allows a programmer to create an object that cannot be modified after construction (immutable objects). If you assign a new object in C# to an immutable object, like say a string. You are getting a new string rather than modifying the original.

What you demonstrated here isn't all that different. You can try a const instead

const x = 6 / 2;
console.log(x);  // 3
 x = 8;
console.log(x); // 3

Reference

Syntax

const varname1 = value1 [, varname2 = value2 [, varname3 = value3 [, ... [, varnameN = valueN]]]];

Browser compatibility

The current implementation of const is a Mozilla-specific extension and is not part of ECMAScript 5. It is supported in Firefox & Chrome (V8). As of Safari 5.1.7 and Opera 12.00, if you define a variable with const in these browsers, you can still change its value later. It is not supported in Internet Explorer 6-9, or in the preview of Internet Explorer 10. The const keyword currently declares the constant in the function scope (like variables declared with var).