MDN may have intermittent access issues April 18 13:00 - April 19 01:00 UTC. See for all notifications.

Your Search Results

    String.indexOf Redirect 1


    The indexOf() method returns the index within the calling String object of the first occurrence of the specified value, starting the search at fromIndex,
    returns -1 if the value is not found.


    str.indexOf(searchValue[, fromIndex])


    A string representing the value to search for.
    The location within the calling string to start the search from. It can be any integer between 0 and the length of the string. The default value is 0.


    Characters in a string are indexed from left to right. The index of the first character is 0, and the index of the last character of a string called stringName is stringName.length - 1.

    "Blue Whale".indexOf("Blue");     // returns  0
    "Blue Whale".indexOf("Blute");    // returns -1
    "Blue Whale".indexOf("Whale", 0); // returns  5
    "Blue Whale".indexOf("Whale", 5); // returns  5
    "Blue Whale".indexOf("", 9);      // returns  9
    "Blue Whale".indexOf("", 10);     // returns 10
    "Blue Whale".indexOf("", 11);     // returns 10


    The indexOf method is case sensitive. For example, the following expression returns -1:

    "Blue Whale".indexOf("blue") // returns -1

    Checking occurrences

    Note that '0' doesn't evaluate to true and '-1' doesn't evaluate to false. Therefore, when checking if a specific string exists within another string the correct way to check would be:

    "Blue Whale".indexOf("Blue") != -1; // true
    "Blue Whale".indexOf("Bloe") != -1; // false


    Example: Using indexOf and lastIndexOf

    The following example uses indexOf and lastIndexOf to locate values in the string "Brave new world".

    var anyString = "Brave new world";
    console.log("The index of the first w from the beginning is " + anyString.indexOf("w"));
    // Displays 8
    console.log("The index of the first w from the end is " + anyString.lastIndexOf("w")); 
    // Displays 10
    console.log("The index of 'new' from the beginning is " + anyString.indexOf("new"));   
    // Displays 6
    console.log("The index of 'new' from the end is " + anyString.lastIndexOf("new"));
    // Displays 6

    Example: indexOf and case-sensitivity

    The following example defines two string variables. The variables contain the same string except that the second string contains uppercase letters. The first log method displays 19. But because the indexOf method is case sensitive, the string "cheddar" is not found in myCapString, so the second log method displays -1.

    var myString    = "brie, pepper jack, cheddar";
    var myCapString = "Brie, Pepper Jack, Cheddar";
    console.log('myString.indexOf("cheddar") is ' + myString.indexOf("cheddar"));    
    // Displays 19
    console.log('myCapString.indexOf("cheddar") is ' + myCapString.indexOf("cheddar")); 
    // Displays -1

    Example: Using indexOf to count occurrences of a letter in a string

    The following example sets count to the number of occurrences of the letter x in the string str:

    count = 0;
    pos = str.indexOf("x");
    while ( pos != -1 ) {
       pos = str.indexOf( "x",pos + 1 );


    Specification Status Comment
    ECMAScript 1st Edition. Standard Initial definition.
    ECMAScript Language Specification 5.1th Edition (ECMA-262) Standard  
    ECMAScript Language Specification 6th Edition (ECMA-262) Draft  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Document Tags and Contributors

    Contributors to this page: Sheppy
    Last updated by: Sheppy,
    Hide Sidebar