ES6/constant

const.js

// `const` creates an 'immutable variable', that is a variables which cannot be 
// re-assigned new content. Note this only makes the variable itself immutable, 
// not its assigned content (for instance, in case the content is an object, 
// this means the object itself can still be altered).
const PI = 3.14159;

// `let` creates a variable that is scoped to its nearest containing block.
// Compare this to `var` which scopes a variable to its nearest containing
// function.
let name = "Steve";

// It's good practice to use either `const` or `let` in lieu of `var` if
// ES6 is available.