14 Important JavaScript Functions Every Web Developer Should Know - https://medium.com/javascript-in-plain-english/14-important-javascript-functions-every-web-developer-should-know-e34169ae91c8

14-important-js-functions-every-web-developer-should-know.js

// 1. Max Number
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);

maxN([1, 2, 3, 4]);         // [4]
maxN([2, 4, 6, 4, 3], 2);   // [6, 4]


// 2. Ternary Operator
function temparature(temp) {
    return temp > 39 || temp < 35.5
        ? 'Visit Doctor!'
        : temp < 37.5 && temp > 36.5
        ? 'Go Out and Play!!'
        : temp <= 39 && temp >= 35.5
        ? 'Take Some Rest!'
        : '';
}

console.log(temparature(38));   // Take Some Rest!
console.log(temparature(36));   // Take Some Rest!
console.log(temparature(39.1)); // Visit Doctor!
console.log(temparature(35.1)); // Visit Doctor!
console.log(temparature(37));   // Go Out and Play


// 3. Remove duplicates from an array
function removeDuplicates(array) {
    return [...new Set(array)];
}

const uniqueStr = removeDuplicates(['Paul', 'John', 'Harald', 'Paul', 'John']);
const uniqueNr = removeDuplicates([1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 7, 7, 9]);
console.log(uniqueStr);     // [ 'Paul', 'John', 'Harald' ]
console.log(uniqueNr);      // [1, 2, 3, 4, 5, 6, 7, 9]


// 4. Find a specific object in an array
const employess = [
    { name: 'Paul', job_title: 'Software Engineer' },
    { name: 'Peter', job_title: 'Web Developer' },
    { name: 'Harald', job_title: 'Screen Designer' },
];
let sen = employess.find((data) => data.job_title === 'Software Engineer');

console.log(sen); // { name: 'Paul', job_title: 'Software Engineer' }


// 5. Decapitalize
const decapitalize = ([first, ...rest]) => first.toLowerCase() + rest.join('');

decapitalize('CamelCase');  // camelCase
decapitalize('Super');      // super


// 6. Reverse a String
const reverse = (input) => {
    return input.split('').reverse().join('');
};

console.log(reverse('Paul Knulst'));        // tslunK luaP
console.log(reverse('Twitter is awesome')); // emosewa si rettiwT


// 7. Calculate the Day of the Year
const dayOfYear = (date) =>
    Math.floor(
        (date - new Date(date.getFullYear(), 0, 0)) / 1000 / 60 / 60 / 24
    );

dayOfYear(new Date()); // 350


// 8. Convert an array to an HTML list element
const arrayToHtmlList = (arr, listID) =>
    ((el) => (
        (el = document.querySelector('#' + listID)),
        (el.innerHTML += arr.map((item) => `<li>${item}</li>`).join(''))
    ))();

arrayToHtmlList(['item 1', 'item 2'], 'myListID');


// 9. Shorten the console log
const log = console.log.bind(document);
const error = console.error.bind(document);

log('does it work?');
log('yes');
error('something bad happened');


// 10. Get a sample size from an input arrayconst sampleSize = ([...arr], n = 1) => {
    let m = arr.length;
    while (m) {
        const i = Math.floor(Math.random() * m--);
        [arr[m], arr[i]] = [arr[i], arr[m]];
    }
    return arr.slice(0, n);
};

sampleSize([6, 7, 9, 2, 1], 2);             // [9, 1]
sampleSize([5, 7, 2, 3, 4, 1, 8, 9], 4);    // [7, 8, 9, 5]
sampleSize([5, 4, 6], 4);                   // [6, 5, 4]


// 11. Destructuring in JavaScript
const arr = ['Paul', 'Knulst', 'Software Engineer', 'Challenger'];
const [firstName, surname, ...rest] = arr;

console.log(firstName);     // Paul
console.log(surname);       // Knulst
console.log(rest);          // ["Software Engineer", "Challenger"]

// …Actually, we can use it with any iterable, not only arrays:
let [a, b, c] = 'abc';                      // a = "a", b = "b", c = "c"
let [one, two, three] = new Set([1, 2, 3]); // one = 1, two = 2, three = 3


// 12. Deep flatten an array
const deepFlatten = (arr) =>
    [].concat(...arr.map((v) => (Array.isArray(v) ? deepFlatten(v) : v)));

deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]


// 13. Find multiple indexes within an array
const indexOfAll = (arr, val) =>
    arr.reduce((acc, el, i) => (el === val ? [...acc, i] : acc), []);

indexOfAll([1, 2, 3, 1, 2, 3], 1); // [0,3]
indexOfAll([1, 2, 3], 4);           // []


// 14. Check if the object is a specific type
const is = (type, val) => ![, null].includes(val) && val.constructor === type;

is(Array, [1]);         // true
is(Array, 'hello');     // false
is(Map, new Map());     // true
is(Map, [2]);           // false
is(RegExp, /./g);       // true
is(Set, new Set());     // true

This Gist contains every example mentioned in this article: https://medium.com/javascript-in-plain-english/14-important-javascript-functions-every-web-developer-should-know-e34169ae91c8