- Part of JavaScript's String object, indexOf() quickly checks if characters you pass as argument are contained in another piece of text. The method returns the start position index (integer):
var str = "I learn JavaScript";
alert( str.indexOf("I learn") ); // zero (first character position index)
alert( str.indexOf("learn") ); // 2Note: indexOf() searches from the left (beginning of string), and stops after the first instance.
- JavaScript returns -1 if the string is not found:
var str = "I learn JavaScript";
alert( str.indexOf("carrot") ); // Not found: returns -1 - You can test directly against a literal string (no variable needed!)
alert( "I learn JavaScript".indexOf("ear") ); // returns 3Tip - to use indexOf() as boolean condition, check if the returned value is greater than -1:
if( "I learn JavaScript".indexOf("learn") > -1 ) // True if found
alert( "The string was found!" ); - indexOf() is case-sensitive: use toLowerCase() or toUpperCase() to temporarily convert letter casing - this allows JavaScript to ignore capitalization during the search:
var str = "I learn JavaScript";
alert( str.indexOf("javascript") ); // case mismatch → returns -1
alert( str.toLowerCase().indexOf("javascript") ); // Found, returns 8 - To start searching *after* the beginning of the string, supply an alternate start index: this saves you the step of using substring(), and still returns the real position index (substring highlighted).
// Not passing second argument same as passing zero:
alert( "I learn JavaScript".indexOf("ear",0) ); // 3
alert( "I learn JavaScript".indexOf("ear",2) ); // 3
alert( "I learn JavaScript".indexOf("ear",3) ); // 3
alert( "I learn JavaScript".indexOf("ear",4) ); // Not found, returns -1Note: optional index must be between zero and String.length-1 (last character's position index).
- Practical example: get current URL's directory, excluding "http://" from the search:
var str = document.URL;
alert( str.substring( str.indexOf("/",7) , str.lastIndexOf("/")+1 ) ); Tip: to search with regular expressions (text pattern matching), use the search() method.
- The PHP equivalent to JavaScript's indexOf() method is the strpos() function: PHP works around the case-sensitivity issue by also supporting a stripos() function, which ignores capitalization.
$str = 'I learn PHP';
echo strpos( $str , 'php' ); // Not found, returns 'FALSE'
echo stripos( $str , 'php' ); // Case-insensitive search, returns 8 Sister method: lastIndexOf() looks for one string in another, but starts from the end (right side).
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