ES6 —  métodos para manipulação de strings

inclues.js

 let text = 'JavaScript is cool ';
 console.log(text.includes('is')); 

repeat.js

 console.log('JavaScript Level God '.repeat(10));

startsWith.js

 let text = 'JavaScript is cool ';
 console.log(text.startsWith('JavaScript')); 

startsWithInPosition.js

 let text = 'JavaScript is cool ';
 console.log(text.startsWith('JavaScript', 4));