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Javascript Advanced

The + Operator

  • converting the given expression to a number
+(new Date())	// 1593565210654

+true // 1
+false // 0

+"1e-8" // 100000000
+"1.6e-2" // 0.016


// overriding the valueOf() method of the random object
const random = {
  'valueOf': () => Math.floor(Math.random() * 1000)
}

+random // 42
+random // 476
+random // 887

The Comma Operator

  • evaluate multiple expressions where JavaScript expects one
let money = 10;
const hasStudied = false;
const relax = () => console.log("relax");
const study = () => console.log("study");
hasStudied ? (money++, relax()) : (money/=2, study());	// study

console.log(money);	// 5

for (let i=1, j=2; i+j < 10; i++, j++) {
  console.log(i, j);
}
// 1 2
// 2 3
// 3 4
// 4 5

const coins = [
  {value:4, currency:"EUR"},
  {value:1, currency:"USD"},
  {value:5, currency:"BTC"},
]
const countOddCoins = (coins) => {
  let oddCoins = 0;
  coins.forEach(({ value, currency }) => {
    if (value % 2 != 0) {
      (oddCoins++, console.log(`${oddCoins} with ${currency}`));
    }
  })
  return oddCoins;
}
console.log(countOddCoins(coins));
// 1 with USD
// 5 with BTC
// 2

The Set Object

  • stores unique values of any type, whether primitive values or object references
const arr = [1, 1, 7, 5, 6, 6, 6, 8, 7];
// old way
let noDup = arr.filter((a,b) => arr.indexOf(a) === b);
// new way
noDup = [...new Set(arr)];
console.log(noDup);
// 1 7 5 6 8

let a = new Set("hello world!");
// h e l o w r d !
let b = new Set("medium is cool!");
// m e d i u m s c o l !

const intersection = (a, b) => {
  let intersection = new Set();
  for (let elem of b) {
    if (a.has(elem)) {
      intersection.add(elem);
    }
  }
  return intersection;
}
console.log(intersection(a, b));
// e d o l !

The Navigator & Performance API's

const webapi = () => {
    // Performance API
    const start = performance.now();
    const fib = n => {
        if(n <= 1) return n;
        return fib(n-1) + fib(n-2);
    }
    fib(15);
    const end = performance.now();
    console.log(end - start);
    // 0.1699999994598329 (on my machine)

    // Navigator API
    navigator.geolocation.getCurrentPosition(pos => {
        const { coords: { latitude, longitude } } = pos;
        console.log(latitude, longitude);
        // 48.9080891 2.2699974
    });
}

recude() map() and filter()

let orders = [1, 2, 3, 4, 5];
const total = orders.reduce((acc, cur) => acc + cur);
console.log(total);		// 15

const total2 = orders.map((item) => item*2);
console.log(total2);	// 2, 4, 6, 8, 10

const total3 = orders.filter((item) => item > 3);
console.log(total3);	// 4, 5

Shuffle Array Elements

const arr = [1, 2, 3, 4, 5];
const shuffled = arr.sort(() => Math.random() - 0.5);
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