JavaScript CS

javascript.md

// JavaScript CS

// convert to string
// --------------------------------------------------------------------

let myNumber = 9;

let myString = String(score);

// convert to number
// --------------------------------------------------------------------

let myString = '44';

let myNumber = Number(myString);

// convert to boolean
// --------------------------------------------------------------------

let age = 0;

// good
let hasAge = Boolean(age);

// best
let hasAge = !!age;

// array map - Array.prototype.map()
// --------------------------------------------------------------------

let numbers = [1, 5, 10, 15];
let doubles = numbers.map(function(x) {
   return x * 2;
});
// doubles is now [2, 10, 20, 30]
// numbers is still [1, 5, 10, 15]

// es6 example
let numbers = [2, 4, 8, 10];
let halves = numbers.map(x => x / 2);
// halves is now [1, 2, 4, 5]
// numbers is still [2, 4, 8, 10]

let numbers = [1, 4, 9];
let roots = numbers.map(Math.sqrt);
// roots is now [1, 2, 3]
// numbers is still [1, 4, 9]


// array filter - Array.prototype.filter()
// --------------------------------------------------------------------

let words = ["spray", "limit", "elite", "exuberant", "destruction", "present", "happy"];

let longWords = words.filter(function(word){
  return word.length > 6;
});

// filtered array longWords is ["exuberant", "destruction", "present"]

// array find - Array.prototype.find()
// --------------------------------------------------------------------

function isBigEnough(element) {
  return element >= 15;
}

[12, 5, 8, 130, 44].find(isBigEnough); // 130

// array slice - Array.prototype.slice()
// --------------------------------------------------------------------

let a = ['zero', 'one', 'two', 'three'];
let sliced = a.slice(1, 3);

console.log(a);      // ['zero', 'one', 'two', 'three']
console.log(sliced); // ['one', 'two']


// array splice - Array.prototype.splice()
// --------------------------------------------------------------------

let myFish = ['angel', 'clown', 'mandarin', 'sturgeon'];

myFish.splice(2, 0, 'drum'); // insert 'drum' at 2-index position
// myFish is ["angel", "clown", "drum", "mandarin", "sturgeon"]

myFish.splice(2, 1); // remove 1 item at 2-index position (that is, "drum")
// myFish is ["angel", "clown", "mandarin", "sturgeon"]