JavaScript data type
May 06, 2021 JavaScript
Table of contents
2. JavaScript has a dynamic type
12.. Declare the variable type
JavaScript data type
String, Number, Boolean, Array, Object, Null, Undefined.
JavaScript has a dynamic type
JavaScript has a dynamic type. This means that the same variables can be used as different types:
VAR x = 5; // Now x is a number
Var x = "john"; // Now x is a string
JavaScript string
A string is a variable that stores characters, such as "Bill Gates."
Strings can be any text in quotation marks. You can use single or double quotes:
var carname='Volvo XC60';
You can use quotation marks in strings as long as they do not match the quotation marks that surround the string:
var answer="He is called 'Johnny'";
var answer='He is called "Johnny"';
Try it out . . .
You'll learn more about strings in the advanced part of this tutorial.
JavaScript numbers
JavaScript has only one type of number.
Numbers can be taken with or without:
VAR X2 = 34; // Do not write to the decimal point
Large or very small numbers can be written by scientific (exponential) counting:
You'll learn more about numbers in the advanced part of this tutorial.
JavaScript Boolean
Boolean (logic) can only have two values: true or false.
var y=false;
Boolean is commonly used in conditional testing. You'll learn more about conditional testing later in this tutorial.
JavaScript array
The following code creates an array named cars:
cars[0]="Saab";
cars[1]="Volvo";
cars[2]="BMW";
Or (the resulted array):
Or (literal array):
The array undersrage is zero-based, so the first item is .0, the second is .1, and so on.
You'll learn more about arrays later in this tutorial.
JavaScript object
Objects are separated by parentheses. I nside the parenthesis, the properties of the object are defined as a name and value pair (name: value). The property is separated by a comma:
The object (person) in the example above has three properties: firstname, lastname, and id.
Spaces and folds don't matter. Declarations can span multiple lines:
firstname : "John",
lastname : "Doe",
id : 5566
};
Object properties are addressed in two ways:
You'll learn more about objects later in this tutorial.
Undefined and Null
The value of Undefined indicates that the variable does not contain a value.
You can empty a variable by setting its value to null.
Declare the variable type
When you declare a new variable, you can use the keyword "new" to declare its type:
var y= new Boolean;
var cars= new Array;
var person= new Object;
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JavaScript variables are objects. When you declare a variable, a new object is created. |
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Tip: JavaScript has an implicit global concept, which means that any variable you don't declare becomes a global object property.
JavaScript Data Type Learning Brain Map:
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JavaScript Standard Reference Tutorial: JavaScript Data Type