immutable values

let a = {
    foo: 'bar'
};

let b = a;

a.foo = 'test';

console.log(b.foo); // test
console.log(a === b) // true
let a = 'test';
let b = a;
a = a.substring(2);

console.log(a) //st
console.log(b) //test
console.log(a === b) //false
let a = ['foo', 'bar'];
let b = a;

a.push('baz')

console.log(b); // ['foo', 'bar', 'baz']

console.log(a === b) // true
let a = 1;
let b = a;
a++;

console.log(a) //2
console.log(b) //1
console.log(a === b) //false