JavaScript Learning notes (3)

Data types for JavaScript

Character type, number, Boolean, array, object, Null, Undefined

Definition of the array:

var cars=new Array ();

Cars[0]= "Audi";

Cras[1]= "BMW";

Cars[3]= "Benze";

Or:

var cars = new Array ("Audi", "BMW", "Benze");

Or:

var cars =["Audi", "Audi", "Audi", "Audi", "Audi";

Such as:

<! DOCTYPE html>

<body>

<script>
var i;
Mode 1
var cars1 = new Array ();
Cars1[0] = "Audi";
CARS1[1] = "BMW";
CARS1[2] = "Volvo";

Mode 2:
var cars2 = new Array ("Audi", "BMW", "Volvo", "Audi", "BMW", "Volvo");

Mode 3
var cars3=["Audi", "Audi", "Audi", "Audi", "Audi";

for (i=0;i<cars3.length;i++)
{
document.write (Cars3[i] + "<br>");
}
</script>

</body>

JavaScript objects

Objects are separated by curly braces. Inside the parentheses, the properties of the object are defined in the form of name and value pairs (name:value). Attributes are separated by commas:
var person={firstname: "Bill", LastName: "Gates", id:5566};
The object (person) in the example above has three attributes: FirstName, LastName, and ID.
Spaces and lines do not matter. Declarations can span multiple lines:
var person={
FirstName: "Bill,"
LastName: "Gates",
id:5566
};
Object properties are addressed in two ways:

Name=person.lastname;

name=person["LastName"];

Such as:

<! DOCTYPE html>

<body>

<script>
var person={
FirstName: "Bill,"
LastName: "Gates",
id:5566
};

document.write (person.firstname+ "+person.lastname" + "+person.id+" <br/> ");
document.write (person["FirstName"]+ "+person[" LastName "]+" to "+person[" "id"] + "<br/>");
</script>

</body>

Undefined and Null

Undefined this value means that the variable does not contain a value

Null can be used to empty variables

Such as:

<! DOCTYPE html>

<body>

<script>
var person;
var car= "Volvo";
document.write (person + "<br/>");
document.write (car + "<br/>" + "<br/>");

var car=null
var person= "Steve Jobs";
document.write (person + "<br/>");
document.write (car + "<br/>");
</script>

</body>

Output Result:

Undefined
Volvo

Steve Jobs
Null

Declaring variable types

You can declare the type of a variable by using the New keyword

Such as:

<! DOCTYPE html>

<body>

<button onclick= "myFunction ()" > click here </button>

<p id= "Test1" ></p>
<p id= "Test2" ></p>
<p id= "Test3" ></p>
<p id= "Test4" ></p>

<script>
function MyFunction ()
{
var numval = new number;
Numval = 123.123;

var strval = new String;
Strval = "This is A STRING.";

var bVal = new Boolean;
BVal = true;

var arrval = new Array;
arrval[0]=100;
arrval[2]=200;
arrval[3]=300;
arrval[4]=400;
arrval[5]=500;

document.getElementById ("Test1"). Innerhtml=numval;
document.getElementById ("Test2"). Innerhtml=strval;
document.getElementById ("Test3"). Innerhtml=bval;
document.getElementById ("Test4"). Innerhtml=arrval[3];
}
</script>

</body>

Output Result:

<! DOCTYPE html>

<body>

<button onclick= "myFunction ()" > click here </button>

<p id= "Test1" ></p>
<p id= "Test2" ></p>
<p id= "Test3" ></p>
<p id= "Test4" ></p>

<script>
function MyFunction ()
{
var numval = new number;
Numval = 123.123;

var strval = new String;
Strval = "This is A STRING.";

var bVal = new Boolean;
BVal = true;

var arrval = new Array;
arrval[0]=100;
arrval[2]=200;
arrval[3]=300;
arrval[4]=400;
arrval[5]=500;

document.getElementById ("Test1"). Innerhtml=numval;
document.getElementById ("Test2"). Innerhtml=strval;
document.getElementById ("Test3"). Innerhtml=bval;
document.getElementById ("Test4"). Innerhtml=arrval[3];
}
</script>

</body>

Click the button to output the result:

123.123

This is A STRING.

True

300

JavaScript Learning notes (3)