Core JavaScript 1.5 Reference:Global Objects:String:indexOf
From MDC
Contents |
[edit] Summary
Returns the index within the calling String object of the first occurrence of the specified value, starting the search at fromIndex, or -1 if the value is not found.
| Method of String | |
| Implemented in: | JavaScript 1.0, NES2.0 |
| ECMA Version: | ECMA-262 |
[edit] Syntax
indexOf(searchValue[, fromIndex])
[edit] Parameters
-
searchValue - A string representing the value to search for.
-
fromIndex - 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.
[edit] Description
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")
[edit] Examples
[edit] 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"
document.write("<P>The index of the first w from the beginning is " +
anyString.indexOf("w")) // Displays 8
document.write("<P>The index of the first w from the end is " +
anyString.lastIndexOf("w")) // Displays 10
document.write("<P>The index of 'new' from the beginning is " +
anyString.indexOf("new")) // Displays 6
document.write("<P>The index of 'new' from the end is " +
anyString.lastIndexOf("new")) // Displays 6
[edit] 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 writeln method displays 19. But because the indexOf method is case sensitive, the string "cheddar" is not found in myCapString, so the second writeln method displays -1.
myString="brie, pepper jack, cheddar"
myCapString="Brie, Pepper Jack, Cheddar"
document.writeln('myString.indexOf("cheddar") is ' +
myString.indexOf("cheddar"))
document.writeln('<P>myCapString.indexOf("cheddar") is ' +
myCapString.indexOf("cheddar"))
[edit] 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 ) {
count++;
pos = str.indexOf("x",pos+1);
}