String methods help you to work with strings.

String Methods and Properties

Primitive values, like "John Doe", cannot have properties or methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.

String Length

The length property returns the length of a string:

Finding a String in a String

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

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

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:

Searching for a String in a String

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

Did You Notice?

The two methods, indexOf() and search(), are equal?

They accept the same arguments (parameters), and return the same value?

The two methods are quite equal. These are the differences:

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

You will learn more about regular expressions in a later chapter.

Extracting String Parts

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

• slice(start, end)
• substring(start, end)
• substr(start, length)

The slice() Method

slice() extracts a part of a string and returns the extracted part in a new string.

The method takes 2 parameters: the starting index (position), and the ending index (position).

This example slices out a portion of a string from position 7 to position 13:

If a parameter is negative, the position is counted from the end of the string.

This example slices out a portion of a string from position -12 to position -6:

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

or, counting from the end:

The substring() Method

substring() is similar to slice().

The difference is that substring() cannot accept negative indexes.

If you omit the second parameter, substring() will slice out the rest of the string.

The substr() Method

substr() is similar to slice().

The difference is that the second parameter specifies the length of the extracted part.

If the first parameter is negative, the position counts from the end of the string.

The second parameter can not be negative, because it defines the length.

If you omit the second parameter, substr() will slice out the rest of the string.

Replacing String Content

The replace() method replaces a specified value with another value in a string:

By default, the replace() function replaces only the first match:

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

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):

Converting to Upper and Lower Case

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

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

The concat() Method

concat() joins two or more strings:

The concat() method can be used instead of the plus operator. These two lines do the same:

Extracting String Characters

There are 2 safe methods for extracting string characters:

• charAt(position)
• charCodeAt(position)

The charAt() Method

The charAt() method returns the character at a specified index (position) in a string:

The charCodeAt() Method

The charCodeAt() method returns the unicode of the character at a specified index in a string:

Accessing a String as an Array is Unsafe

You might have seen code like this, accessing a string as an array:

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.

Converting a String to an Array

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

If the separator is omitted, the returned array will contain the whole string in index [0].

If the separator is "", the returned array will be an array of single characters:

JavaScript String Reference

JavaScript Strings

A JavaScript string stores a series of characters like "John Doe".

A string can be any text inside double or single quotes:

String indexes are zero-based: The first character is in position 0, the second in 1, and so on.

String Properties and Methods

Primitive values, like "John Doe", cannot have properties or methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.

String Properties

String Methods

String HTML Wrapper Methods

The HTML wrapper methods return the string wrapped inside the appropriate HTML tag.

These are not standard methods, and may not work as expected in all browsers.