The JavaScript indexof method returns the index position of the first occurrence of a specified string. If the specified string not located, the indexof function will return -1. The syntax of the JavaScript indexof function is
String_Object.indexof(Substring, Starting_Position)
- String_Object: Valid String Object or literal.
- Substring: String you want to search inside the string_Object.
- Starting_Position: This is an optional parameter. If you want to specify the starting point (starting index position), then please specify the index value here.
NOTE:
- If the Starting_Position is a Negative number, JavaScript IndexOf starts looking from Zero.
- If the Starting_Position is Out of range Index, IndexOf function start looking from the highest index number.
JavaScript indexof Example
The following set of examples will help you understand the indexof Function.
<!DOCTYPE html> <html> <head> <title> JavaScript IndexOf </title> </head> <body> <h1> JavaScript IndexOf </h1> <script> var Str1 = "Learn JavaScript at Tutorial Gateway.org"; var Str2 = "We are abc working at abc company"; var Str3 = Str1.indexOf("Script"); var Str4 = Str1.indexOf("abc"); // Non existing item var Str5 = Str2.indexOf("abc"); var Str6 = Str1.indexOf("Script", 5); var Str7 = Str2.indexOf("abc", 10); document.write("<b> Index position of Script is:</b> " + Str3); document.write("<br \> <b> Index position of abc is:</b> " + Str4); document.write("<br \> <b> Index position of abc is:</b> " + Str5); document.write("<br \> <b> Index position of Script is:</b> " + Str6); document.write("<br \> <b> Index position of abc is:</b> " + Str7); </script> </body> </html>
TIP: The index position in JavaScript indexof Function will start from 0, Not 1.
The following statement finds the index position of a substring ‘Script’ and stores the index value in Str3.
var Str3 = Str1.indexOf("Script");
In the next line, we are looking for a non-existing “abc” inside the Str1. Since JS indexof function doesn’t find the substring, it is returning -1 as output
var Str4 = Str1.indexOf("abc"); // Non existing item
Here, we are looking for “abc” inside the Str2 using IndexOf function.
var Str5 = Str2.indexOf("abc");
From the above statement, though abc reappeared multiple times, the Javascript indexof function written the index position of a first occurrence. Now, let us modify the starting position from default 0 to 10
var Str7 = Str2.indexOf("abc", 10);
The above code returns the first occurrence of string abc starting at index position 10.