Array.prototype.indexOf() vs String.prototype.indexOf()

 

Array.prototype.indexOf()

const beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];

console.log(beasts.indexOf('bison'));
// expected output: 1

// start from index 2
console.log(beasts.indexOf('bison', 2)); // ** index 2에서부터 찾아라!
// expected output: 4

console.log(beasts.indexOf('giraffe'));
// expected output: -1

 

String.prototype.indexOf()

const paragraph = 'The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?';

const searchTerm = 'dog';
const indexOfFirst = paragraph.indexOf(searchTerm);

console.log('The index of the first "' + searchTerm + '" from the beginning is ' + indexOfFirst);
// expected output: "The index of the first "dog" from the beginning is 40"

console.log('The index of the 2nd "' + searchTerm + '" is ' + paragraph.indexOf(searchTerm, (indexOfFirst + 1)));
// expected output: "The index of the 2nd "dog" is 52"