7 best JavaScript tricks you won’t be able to live without!

Arnaud Dostes

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2 min read

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Sep 6, 2019

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1. Use destructuring to swap variables

let a = 1;
let b = 2;
console.log(a, b); // 1 2
[a, b] = [b, a]; // Magic swap!
console.log(a, b); // 2 1

2. Use the Spread operator to create a function that accepts a variable number of arguments

const add = (...numbers) => { // numbers is an array!
  const sum = numbers.reduce((sum, n) => sum + n, 0);
  return sum;
};
let sum = add(1, 2, 3);
console.log(sum); // 6
sum = add(1, 2, 3, 4); // as many as I want!!!
console.log(sum); // 10

3. Use the Spread operator to conditionally add a property to an object

const add = true;
const dontAdd = false;
const obj = {
  a: 1,
  ...(add && { b: 2 }), // will be added
  ...(dontAdd && { c: 3 }) // will NOT be added!!!!
};
console.log(obj); // { a: 1, b: 2 }

4. Use the Spread operator to eliminate duplicate values in an array!

const a = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5];
const uniques = [...new Set(a)]; // to Set and back to array!
console.log(uniques); // [ 1, 2, 3, 4, 5 ]

5. Destructure objects with defaults

let o = { a: 1 };
let { a, b = 2 } = o;
console.log(a, b); // 1 2 -> b is not undefined!

6. Destructure arrays with defaults

let array = [0, 1, 2];
let [a, b, c, d = 3] = array;
console.log(a, b, c, d); // 0 1 2 3 -> d is not undefined!

7. Filter falsy values

let array = [{}, [], 0, '', true, false, undefined, null, NaN];
console.log(...array.filter(Boolean)); // {} [] true

8. BONUS!!! Use JSON.stringify to pretty print in the console

let obj = { a: 1, b: 2, c: { d: { value: 3 } }, e: [1, 2, 3] };console.log(JSON.stringify(obj)); 
// Prints: {"a":1,"b":2,"c":{"d":{"value":3}},"e":[1,2,3]}console.log(JSON.stringify(obj, null, 2)); // Better!
/*
Prints:
{
  "a": 1,
  "b": 2,
  "c": {
    "d": {
      "value": 3
    }
  },
  "e": [
    1,
    2,
    3
  ]
}
*/

9. BONUS BONUS! Use console.time to track how long something takes

console.time('increment');
let n = 0;
for (let i = 0; i < 1000000; i += 1) {
  n += i;
}
console.timeLog('increment'); // 0.349ms -> intermediate time
for (let i = 0; i < 1000000; i += 1) {
  n += i;
}
console.timeEnd('increment'); // 0.808ms -> total time