Javascript Tutorial 13 String Methods

The indexOf() method returns the index of (the position of) the first occurrence of a specified text in a string and the lastIndexOf() method returns the index of the last occurrence of a specified text in a string:

var str = "Please locate where 'locate' occurs!";
var pos1 = str.indexOf("locate");     // 7
var pos2 = str.lastIndexOf("locate"); // 21

Both the indexOf(), and the lastIndexOf() methods return -1 if the text is not found.

Both methods accept a second parameter as the starting position for the search:

var str = "Please locate where 'locate' occurs!";
var pos = str.indexOf("locate", 15);     // 21

The search() method searches a string for a specified value and returns the position of the match:

var str = "Please locate where 'locate' occurs!";
var pos = str.search("locate");

indexOf() and search() are quite equal. These are the differences between indexOf() and search():

• The search() method cannot take a second start position argument.
• The search() method can take much more powerful search values (regular expressions).

There are 3 methods for extracting a part of a string:

• slice(start, end)
• substring(start, end)
  • substring() is similar to slice().
  • The difference is that substring() cannot accept negative indexes.
• substr(start, length)
  • substr() is similar to slice().
  • The difference is that the second parameter specifies the length of the extracted part.
  • If you omit the second parameter, substr() will slice out the rest of the string.

var str = "Apple, Banana, Kiwi";
var res1 = str.slice(7, 13);   // Banana
var res2 = str.slice(-12, -6); // Banana

If you omit the second parameter, the method will slice out the rest of the string:

var str = "Apple, Banana, Kiwi";
var res1 = str.slice(7);    // Banana, Kiwi
var res2 = str.slice(-12);  // Banana, Kiwi

Negative positions do not work in Internet Explorer 8 and earlier.

The replace() method replaces a specified value with another value in a string. By default, the replace() function replaces only the first match:

str = "Please visit Microsoft and Microsoft!";
var n = str.replace("Microsoft", "W3Schools");  // Please visit W3Schools and Microsoft!

To replace all matches, use a regular expression with a /g flag (global match):

var n = str.replace(/Microsoft/g, "W3Schools"); // Please visit W3Schools and W3Schools!

By default, the replace() function is case sensitive. Writing MICROSOFT (with upper-case) will not work. To replace case insensitive, use a regular expression with an /i flag (insensitive):

var n = str.replace(/MICROSOFT/i, "W3Schools"); // Please visit W3Schools and Microsoft!

The replace() method does not change the string it is called on. It returns a new string.

A string is converted to upper case with toUpperCase().

A string is converted to lower case with toLowerCase().

There are 2 safe methods for extracting string characters:

• charAt(position)
• charCodeAt(position)

var str = "HELLO WORLD";
str.charAt(0);      // returns H
str.charCodeAt(0);  // returns 72

unsafe method:

str[0];             // returns H

This is unsafe and unpredictable:

• It does not work in all browsers (not in IE5, IE6, IE7)
• It makes strings look like arrays (but they are not)
• str[0] = “H” does not give an error (but does not work)

If you want to read a string as an array, convert it to an array first.

A string can be converted to an array with the split() method:

var txt = "ab,cd e";      // String
txt.split(",");           // ["ab", "cd e"]
txt.split(" ");           // ["ab,cd", "e"]
txt.split("");            // ["a", "b", ",", "c", "d", " ", "e"]
txt.split();              // ["ab,cd e"]