Module 1 - Day 4

JS Advanced Array methods map(), reduce()

Contents

JS | Array advanced methods: .map(), .reduce(). JS | Reference VS value / Shadow copy VS deep copy

Advanced Array methods

The .map() and .reduce() methods are methods of the Array object that do not mutate the original array.

• The .map() method:
  • Receives a function as an argument.
  • Returns a manipulated array of the same length as the original.
  • Transfers to each position of the resulting array the return of the argument function.

    const values = [2, 4, 6] const doubledValues = [2, 4, 6].
    const doubledValues = values.map(elm => elm * 2) // [4, 8, 12].

• The .reduce() method:
  • Receives as an argument a function with two default parameters: accumulator and iterated value.
  • Can receive a second argument as the initial value for the accumulator.
  • Takes as the value of the accumulator for the second and successive iterations the value returned from the previous iteration.

    const values = [2, 4, 6] const sum = values.
    const sum = values.reduce((acc, elm) => acc + elm) // 12 

Truthies VS falsies

The falsie values (null, undefined, false, NaN, 0, '') are rejected by default in conditional structures. Every other value (truthy) is accepted by default.

Deep copy

It is possible to make a deep copy of both an object/array and all objects/arrays inside it through the JSON.parse(JSON.stringify(myArray)) technique (more info: parse, stringify).