toLowerCase and toUpperCase

const king = 'Avi Biter';
king.toLowerCase(); // 'avi biter'
king.toUpperCase(); // 'AVI BITER'

trim

const s1 = 'Shimi Tavoro';
s1.trim(); // 'Shimi Tavoro'

const s2 = '   Shimi Tavoro';
s2.trim(); // 'Shimi Tavoro'

const s3 = '   Shimi Tavoro  ';
s3.trim(); // 'Shimi Tavoro'

includes

const str = 'what is a woman?';
str.includes('woman'); // true
str.includes('catapult'); // false
str.includes('a wom'); // true

indexOf

const str = 'ABCDEFG';
str.indexOf('A'); // 0
str.indexOf('BC'); // 1
str.indexOf('EFG'); // 4

replace and replaceAll

const s1 = 'what is a woman?';
s1.replace('woman', 'catapult'); // 'what is a catapult?'

const s2 = 'avi avi avi';
s2.replace('avi', 'PITA'); // 'PITA avi avi'
s2.replaceAll('avi', 'PITA'); // 'PITA PITA PITA'

concat

const s1 = 'AAA', s2 = 'ZZZ';
s1.concat(s2); // 'AAAZZZ'

slice

          // 0123456789
const str = 'ABCDEFGHIJ';
str.slice(2); // 'CDEFGHIJ'
str.slice(0, 2); // 'AB'
str.slice(1, 3); // 'BC'
str.slice(2, 5); // 'CDE'

split

const s1 = 'AAA@BB@CCCC';
s1.split('@'); // ['AAA', 'BB', 'CCCC']
const s2 = 'nisim%shlomo%david';
s2.split('%'); // ['nisim', 'shlomo', 'david']
const s3 = 'AAA BB CCCC D EEEEEE';
s3.split(' '); // ['AAA', 'BB', 'CCCC', 'D', 'EEEEEE']
const s4 = 'AAAshimi tavoriBBshimi tavoriCCCC';
s4.split('shimi tavori'); // ['AAA', 'BB', 'CCCC']