Technical Documentation

JavaScript Strings

A JavaScript string is zero or more characters written inside quotes.

var x = "John Doe";

You can use single or double quotes:


var carName1 = "Volvo XC60";  // Double quotes 
var carName2 = 'Volvo XC60';  // Single quotes

You can use quotes inside a string, as long as they don't match the quotes surrounding the string:


var answer1 = "It's alright"; 
var answer2 = "He is called 'Johnny'"; 
var answer3 = 'He is called "Johnny"';

String Length

To find the length of a string, use the built-in length property:


var txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
var sln = txt.length;

Escape Character

Because strings must be written within quotes, JavaScript will misunderstand this string:


var x = "We are the so-called "Vikings" from the north.";

The string will be chopped to "We are the so-called ".

The solution to avoid this problem, is to use the backslash escape character.

The backslash (\) escape character turns special characters into string characters:

The sequence \" inserts a double quote in a string:


var x = "We are the so-called \"Vikings\" from the north.";

The sequence \' inserts a single quote in a string:


var x = 'It\'s alright.';

The sequence \\ inserts a backslash in a string:


var x = "The character \\ is called backslash.";

Six other escape sequences are valid in JavaScript:

The 6 escape characters above were originally designed to control typewriters, teletypes, and fax machines. They do not make any sense in HTML.

Breaking Long Code Lines

For best readability, programmers often like to avoid code lines longer than 80 characters.

If a JavaScript statement does not fit on one line, the best place to break it is after an operator


document.getElementById("demo").innerHTML = 
"Hello Dolly!";

You can also break up a code line within a text string with a single backslash:


document.getElementById("demo").innerHTML = "Hello \ 
Dolly!";

The \ method is not the preferred method. It might not have universal support. Some browsers do not allow spaces behind the \ character.

A safer way to break up a string, is to use string addition:


document.getElementById("demo").innerHTML = "Hello " + 
"Dolly!";

Strings Can be Objects 5

Normally, JavaScript strings are primitive values, created from literals:

var firstName = "John";

But strings can also be defined as objects with the keyword new :

var firstName = new String("John");


var x = "John"; 
var y = new String("John"); 

// typeof x will return string 
// typeof y will return object

Don't create strings as objects. It slows down execution speed. The new keyword complicates the code. This can produce some unexpected results:

When using the == operator, equal strings are equal:


var x = "John";         
var y = new String("John"); 

// (x == y) is true because x and y have equal values

When using the === operator, equal strings are not equal, because the === operator expects equality in both type and value.


 var x = "John";      
var y = new String("John"); 

// (x === y) is false because x and y have different types (string and object)

Or even worse. Objects cannot be compared:


var x = new String("John");           
var y = new String("John");	

// (x == y) is false because x and y are different objects


var x = new String("John");        
var y = new String("John");	

// (x === y) is false because x and y are different objects

				Note the difference between (x==y) and (x===y).
				Comparing two JavaScript objects will always return false.
			

Javascript Strings