JAVASCRIPT

indexof vs findindex

/* findIndex vs indexOf methods.
All return -1 when no value is found. */

let myArray = [9, 2, 2, 8, 4, 2, 5, 6, 2, 9];

// findIndex(arg => argCondition): return the first index 
// for which the given function is true.
myArray.findIndex(x => x > 2); // → 3

// indexOf(value): return the value's first index.
myArray.indexOf(2); // → 1

// lastIndexOf(value): return the value's last index.
myArray.lastIndexOf(2); // → 8

// indexOf(value, start): return the value's first index, 
// starting at the given position.
myArray.indexOf(2, 3); // → 5

// lastIndexOf(value, stop): return the value's last index, 
// stopping at the given position.
myArray.lastIndexOf(2, 3); // → 2