Learn JS #12

JavaScript Strings

JavaScript strings are for storing and manipulating text.

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

Example

let text = "John Doe";

You can use single or double quotes:

Example

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

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

Example

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

String Length

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

Example

let text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
let length = text.length;

Escape Character

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

let text = “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:

Code Result Description
\’ Single quote
\” Double quote
\\ \ Backslash

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

Example

let text = "We are the so-called \"Vikings\" from the north.";

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

Example

let text= 'It\'s alright.';

The sequence \\  inserts a backslash in a string:

Example

let text = "The character \\ is called backslash.";

Six other escape sequences are valid in JavaScript:

Code Result
\b Backspace
\f Form Feed
\n New Line
\r Carriage Return
\t Horizontal Tabulator
\v Vertical Tabulator

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:

Example

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

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

Example

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:

Example

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

Note: You cannot break up a code line with a backslash:

Example

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

JavaScript Strings as Objects

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

let x = "John";

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

let y = new String("John");

Example

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

Do not create Strings objects.

The new keyword complicates the code and slows down execution speed.

String objects can produce unexpected results:

When using the == operator, x and y are equal:

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

When using the === operator, x and y are not equal:

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

Note the difference between (x==y) and (x===y).

(x == y) true or false?

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

(x === y) true or false?

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

Note: Comparing two JavaScript objects always returns false.

42 thoughts on “Learn JS #12

Leave a Reply

Your email address will not be published. Required fields are marked *