Suggested Prerequisite Knowledge

The presentation of concepts in this guide assumes the reader is familiar with some JS fundamentals, so take a look below and see how comfortable you are with the concepts.

If you're not comfortable with them, each section has a link to more information about its topic, and if that's not enough, here are some resources for learning more JS:

• Scrimba's Courses
• Codecademy's Courses
• Wes Bos' Courses
• Egghead's Courses

Arrow Functions

MDN: Arrow Functions

const add = (a, b) => a + b

add(4, 5) // 9

Nested Functions

MDN: Nested Functions and Closures

const addExpr = a => b => a + b

addExpr(4)(5) // 9

// or

function addFn(a) {
  return function (b) {
    return a + b
  }
}

addFn(4)(5) // 9

Passing Functions as Arguments (Callbacks)

MDN: First-Class Function

const log = x => console.log(x)

[1, 2, 3].forEach(log)
// 1
// 2
// 3

Map, Filter, & Reduce

MDN: map, filter, and reduce

[1, 2, 3].map(x => x * 2)                      // [2, 4, 6]

[1, 2, 3].filter(x => x % 2 !== 0)             // [1, 3]

[1, 2, 3].reduce((sum, item) => sum + item, 0) // 6

Calling Functions

MDN: Calling Functions

const add5    = x => x + 5
const times10 = x => x * 10
const div2    = x => x / 2

div2(times10(add5(15))) // 100