javascript tricks
let a = [1, 2, 3, 4, 5];
let b = [3, 4, 5, 6, 7];
let result = [...new Set([...a, ...b])]; // [1, 2, 3, 4, 5, 6, 7]
let a = [1, 2, 3, 4, 5];
let b = [2, 3, 4, 6];
let result = a.filter(val => ~b.indexOf(val)); // [2, 3, 4]
let a = [1, 2, 3, 4, 5];
let b = [2, 3, 4, 6];
let result = a.filter(val => !~b.indexOf(val)); // [1, 5]
const a = [
[11],
[7, 15],
[5, 9, 13, 20],
[3, 6, 8, 10, 12, 14, 18, 25]
];
const result = a.reduce((el, acc) => el + acc.join(' ') + '\n', '\n');
// output
/*
11
7 15
5 9 13 20
3 6 8 10 12 14 18 25
*/
let str = str.split('').reverse().join('');
function replaceAt(str, i, char) {
return s.substring(0, i) + char + str.substring(i + 1);
}
// using substring
str.substring(0, str.length - 1);
// using slice
str.slice(0, -1)