Remove duplicates

const dups = [ 'cat', 'dog', 'pig', 'cat']
const removed = [ ...new Set(dups)]

• map - for creating new array
• for each - no new array needed
• for (const element of array) - fastest

const calculateTotal = ( item, { shipping = 10, discount = 0 } = {}) => {}
calculateTotal( item, { shipping: 0 })

• in JS anything that isn't a primitive value like string, number or boolean, such as array and object is passed by reference NOT value

  let c = [1,2] // c === d & c == d both true since d is refernecing c in memory. let d = c

  let c = [1,2] // c === d & c == d are both false since an array/object is checking the memory address and they're both set to different memory addresses. let d = [1,2]