armada-js-es2019-snippets.js

/******************************
 * trimStart & trimEnd
 ******************************/

let message = '   ES2109 meetup    '

message.trimRight()
// '   ES2109 meetup'

message.trimLeft()
// 'ES2109 meetup   '

message.trimRight().trimLeft()
// 'ES2109 meetup'

message.trimStart()
// 'ES2109 meetup   '

message.trimEnd().trimStart()
// 'ES2109 meetup'


/******************************
 * map and flatMap
 ******************************/

let courseStudents = [
    ['Janet', 'Martha', 'Bob', ['Phil', 'Candace']],
    ['Wilson', 'Taylor'],
    ['Edith', 'Jacob', 'Peter', 'Betty']
]

let defaultFlattened = courseStudents.flat()
console.log(defaultFlattened)

let alwaysFlattened = courseStudents.flat(Infinity)
console.log(alwaysFlattened)

// flatMap
let grades = [78, 62, 80, 64]
let flatMapped = grades.map(grade => [grade, grade + 7]).flat()
// [
//  78, 85, 62, 69,
//  80, 87, 64, 71
// ]

let flatMapped = grades.flatMap(grade => [grade, grade + 7])
// [
//  78, 85, 62, 69,
//  80, 87, 64, 71
// ]

/******************************
 * Object.entries & Object.fromEntries
 ******************************/

const students = {
    pera: 20,
    mike: 22,
    zika: 20
}

const studentEntires = Object.entries(students)

console.log(studentEntires)

// convert to array in order to make use of .filter() function

let overTwentyOne = Object.entries(students).filter(([, age]) => {
    return age >= 21
})

console.log(overTwentyOne)

// turn multidimensional array back into an object using loop

const drinkingAgeStudents = {}
for (let [name, age] of overTwentyOne) {
    drinkingAgeStudents[name] = age
}

// Object.fromEntires

const students1 = Object.fromEntries(studentEntires)

console.log(students1)


/******************************
 * Optional catch binding 
 ******************************/

// Earlier
try {
    let parsed = JSON.parse(obj)
} catch (_) {
    // ignore err, or use
    alert('This catch is a catch!')
}

// Now
try {
    let parsed = JSON.parse(obj)
} catch {
    console.log(obj)
}


/******************************
 * Private class fields 
 ******************************/
 
 class Dog {
    #sound = 'Woof! Woof!' // this is private
    field = 'bla'

    makeSound() {
        console.log(this.#sound)
    }
}

// create instance
const doggy = new Dog()
doggy.makeSound() // Woof! Woof!

doggy.myProp

// console.log( tommy.#sound ); // SyntaxError


/******************************
 * Promise.allSettled
 ******************************/
 let p1 = () => new Promise((resolve, reject) => setTimeout(() => resolve('val1'), 2000))

let p2 = () => new Promise((resolve, reject) => setTimeout(() => resolve('val2'), 2000))

let p3 = () => new Promise((resolve, reject) => setTimeout(() => reject('err3'), 2000))

let p = Promise.allSettled([p1(), p2(), p3()]).then(values => console.log(values))

// Output
// [ {status: "fulfilled", value: "val1"}
//   {status: "fulfilled", value: "val2"}
//   {status: "rejected", value: "err3"}
// ]