Javascript Strings

Question 1

JavaScript Strings
JavaScript strings are used for storing and manipulating text.
A JavaScript string is zero or more characters written inside quotes.

var x = “John Doe”; //String written inside quotes

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"';

Answer 1

var x = "John Doe";  // String written inside quotes
document.getElementById("demo").innerHTML = x;

next

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

document.getElementById(“demo”).innerHTML =
carName1 + “ “ + carName2;

next

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

document.getElementById(“demo”).innerHTML =
answer1 + “br>” + answer2 + “br>” + answer3;

Question 2

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

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

Answer 2

var txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
document.getElementById("demo").innerHTML = txt.length;

Question 3

Special Characters
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:

Code Result Description
' ‘ Single quote
" “ Double quote
\ \ Backslash

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.’;
etc etc.

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.

Answer 3

var x = "We are the so-called \"Vikings\" from the north.";
document.getElementById("demo").innerHTML = x; 

displays:
var x = "We are the so-called \"Vikings\" from the north.";
document.getElementById("demo").innerHTML = x;

Question 4

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: Hello Dolly

You can also break up a code line within a text string with a single backslash “": 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 “+”: Hello Dolly

You cannot break up a code line with a backslash “":
Hello Dolly

Answer 4

The best place to break a code line is after an operator or a comma:
document.getElementById(“demo”).innerHTML =
“Hello Dolly!”;

next

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

next

A safer way to break up a string, is to use string addition:
document.getElementById(“demo”).innerHTML = “Hello “ +
“Dolly!”;

next

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

Question 5

Strings Can be Objects
Normally, JavaScript strings are primitive values, created from literals:

var x = “John”;

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

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

Or even worse. Objects cannot be compared:
// (x == y) is false because x and y are different objects

last ex:
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.

Answer 5

var x = "John";        // x is a string
var y = new String("John");  // y is an object

document.getElementById(“demo”).innerHTML =
typeof x + “br>” + typeof y;

displays:
string
object

next

var x = "John";        // x is a string
var y = new String("John");  // y is an object
document.getElementById("demo").innerHTML = (x==y);

displays:
Never Create Strings as objects.
Strings and objects cannot be safely compared.

true

//This is false because one is an object now while the other is a string//

next

var x = "John";        // x is a string
var y = new String("John");  // y is an object
document.getElementById("demo").innerHTML = (x===y);

displays:
Strings and objects cannot be safely compared.
false

next

var x = new String("John");  // x is an object
var y = new String("John");  // y is an object
document.getElementById("demo").innerHTML = (x==y);

displays:
JavaScript objects cannot be compared.

false