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JavaScript - IndexOf

The indexOf() method returns the index of (the position of) the first occurrence of a specified text in a string. If it is NOT found, it will return a -1. 0 is actually the very first position (zero based) so it's possible o is return as a positive test.


let str = "Please locate where 'Hello World' occurs!";
let pos = str.indexOf("Hello World")
document.getElementById("demo1").innerHTML = "The position of Hello World is: " + pos + ".";

let str2 = "Please locate where 'Hello World' occurs!";
let pos2 = str.indexOf("Ricky Bobby");
document.getElementById("demo2").innerHTML = "The position of Ricky Bobby is: " + pos2 + ".";

 

The indexOf() also works with arrays! You can use it to determine if something is found within an array. If it is NOT found, it will return a -1. 0 is actually the very first position (zero based) so it's possible o is return as a positive test.


var fruits = ["Banana", "Orange", "Apple", "Mango"];
var a = fruits.indexOf("Apple");

The result of a will be 2 meaning that "Apple" is located at position 2 in the array.