javascript find an element in array

indexOf - return index of first occurrence:

var beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];
 
console.log(beasts.indexOf('bison')); // expected output: 1
 
// start from index 2
console.log(beasts.indexOf('bison', 2)); // expected output: 4
 
console.log(beasts.indexOf('giraffe')); // expected output: -1