JavaScript Functions Review
Arrow Functions
-Provides a shorter, more concise way to write functions.
-Do not have their own this, and instead has this of scope that contains it.
const someNum = 2;
const doubleNum = num => num * 2; //doubleNum === 4
map
-Takes in callback function, which has access to index of current iteration as arg and calls function on each index, then returns new array containing callback results
const someNums = [2, 3, 4];
const doubleNums = someNums.map(num => num * 2); //[4, 6, 8]
filter
-Takes in callback function, which has access to index of current iteration as arg
-Callback should run a boolean test
-If index passes test, is included in new array returned by filter
const someNums = [2, 3, 4, 5, 6];
const evens = someNums.filter(num => num % 2 == 0); //[2, 4, 6]
reduce
-Takes in callback function, which has access to index of current iteration as arg
-Callback function first two args are accumulator, and item, where accumulator is a value that persists across all callbacks in the reduce iteration and item is the current index value
-First arg to filter is callback function. Second optional arg is initial value for accumulator.
const someNums = [2, 3, 4];
const sum = someNums.reduce((sum, num) => sum + value, 5); //sum === 14 (5 + 2 + 3 + 4)
find
-Takes in callback function, which has access to index of current iteration as arg
-Callback function first arg is current index
-Callback statement should return boolean. First Index to return true is returned by find.
const someNums = [1, 2, 4, 6, 9, 10, 12];
const divisible = someNums.find(num => num % 3 === 0); //6
includes
-Returns boolean, based on whether arg passed in is included in array called on
-First arg is it item to search for. Second optional arg is index to start at.
const someNums = [1, 2, 4, 6, 9, 10];
let includesFour = someNums.includes(4); //true
includesFour = someNums.includes(4, 5); //false, as starts on index 5
