const x = 'const';
const x = 'not-const';

Will give an error: 'constant 'x' has already been defined'

const x = 'const';
x = 'not-const';

// will output 'SECRET'

const x = 'SECRET'
if (x = 'ANOTHER_SECRET') {  // Warning! assigining a value variable in an if condition
    console.log (x)
}

// will output 'ANOTHER_SECRET'

var y = 'SECRET'
if (y = 'ANOTHER_SECRET') {
    console.log (y)
}

// Will throw TypeError: const 'x' has already been declared

const x = "SECRET"

/*  complex code */

var x = 0

// Will reassign y and cause trouble

var y = "SECRET"

/*  complex code */

var y = 0

const pi = 3.1415926535