JavaScript Introduction | Standard Objects | String Methods

String Methods

String methods are methods used for string-related operations defined on the String object.

1. String.fromCharCode()
2. String.fromCodePoint()

String.fromCharCode() Method

This method returns a string composed of characters corresponding to a series of comma-separated Unicode values.

String.fromCharCode(65, 66, 67); // "ABC"

String.fromCodePoint() Method

This method returns a string composed of characters corresponding to a series of comma-separated code points.

String.fromCodePoint(65, 66, 67); // "ABC"
String.fromCodePoint(0x2F804);    // "\uD87E\uDC04"
String.fromCodePoint(194564);     // "\uD87E\uDC04"

The String.fromCodePoint() method is not supported in Safari or Internet Explorer.

JavaScript String Methods

String.prototype Methods

Every String instance inherits methods and properties from String.prototype.
Using these inherited String.prototype methods, you can perform the following string operations.

1. Return positions in a string
2. Return the character at a specified position in a string
3. Extract strings
4. Split strings
5. Concatenate strings
6. Convert string case
7. Remove whitespace around strings
8. Manipulate strings using regular expressions

Because the value of a String instance is immutable, every String method creates and returns a new string as its result.

Finding Positions in a String

The following methods return the position where a specific character or string first appears, or the position where it last appears, in a String instance.

• indexOf()
• lastIndexOf()

These methods can receive the position in the String instance where the search should start as the second argument.
If the specified character or string cannot be found, they return -1.

var str = "abcDEFabc";
str.indexOf('abc');     // 0  -> JavaScript indexes start at 0.
str.indexOf('abcd');    // -1 -> character case is distinguished when comparing strings.
str.indexOf('abc', 3);  // 6  -> starts searching for 'abc' from index 3.
str.lastIndexOf('abc'); // 6
str.lastIndexOf('d');   // -1
str.lastIndexOf('c');   // 8

Returning the Character at a Specified Position

The following methods return the character or character code at the passed index in a String instance.

• charAt()
• charCodeAt()
• codePointAt()

var str = "abcDEFabc";
str.charAt(0);      // a
str.charAt(10);     // empty string -> returns an empty string if the passed index is greater than the string length.
str.charCodeAt(0);  // 97           -> returns the UTF-16 code for 'a'.
str.codePointAt(0); // 97           -> returns the Unicode code point for 'a'.

The codePointAt() method is not supported in Safari or Internet Explorer.

Extracting Strings

The following methods return a new string made by extracting only the characters from the passed start index to just before the end index in a String instance.

• slice()
• substring()
• substr()

var str = "abcDEFabc";
str.slice(2, 6);     // cDEF     -> extracts the string from index 2 through index 5.
str.slice(-4, -2);   // Fa       -> indexes passed as negative values start from the end of the string.
str.slice(2);        // abcDEFab -> extracts to the end of the string if no end index is passed.
str.substring(2, 6); // cDEF
str.substr(2, 4);    // cDEF

Splitting Strings

The following method splits a String instance by a separator and returns the split strings as one array.

• split()

If no separator is passed as an argument, the split() method returns an array of length 1 containing the entire string as a single array element.

var str = "JavaScript is very cool! And useful.";
str.split();    // does nothing if no separator is specified.
str.split("");  // splits by each character ("").
str.split(" "); // splits by spaces (" ").
str.split("!"); // splits by exclamation marks ("!").

Concatenating Strings

The following method returns a new string by concatenating the passed string to a String instance.

• concat()

var str = "JavaScript";
str;                                                // JavaScript
str.concat(" is very cool!");                       // JavaScript is very cool!
str.concat(" is very cool!", " And useful.");       // JavaScript is very cool! And useful.
str;                                                // JavaScript

In the example above, the string in variable str is still the same as at first, even after executing the concat() method several times. In this way, the value of a String instance in JavaScript is immutable. Therefore, every String method creates and returns a new string as its result.

Converting String Case

The following methods return a new string with every character in a String instance converted to uppercase or lowercase.

• toUpperCase()
• toLowerCase()

var str = "JavaScript";
str.toUpperCase(); // JAVASCRIPT
str.toLowerCase(); // javascript

Removing Whitespace Around Strings

The following method returns a new string after removing all whitespace and line break characters (LF, CR, etc.) at both ends of a String instance.

• trim()

The trim() method does not affect the string value of the String instance itself.

var str = "      JavaScript    ";
str.trim();

String Manipulation with Regular Expressions

The following methods use a regular expression passed as an argument to search, match, replace, and perform other operations on a String instance value.

• search()
• match()
• replace()

JavaScript String.prototype Methods