JavaScript basic data type and value type reference type description

Lin Bingwen Evankaka original works. Reprint please specify the source Http://blog.csdn.net/evankaka

Summary: This article mainly discusses the basic data types in JavaScript, as well as the difference and use of value types and reference types

I. Basic data Types

The keyword used in JavaScript to declare variables is VAR, which is different from other programming languages, but JavaScript also contains five basic data types (which can be said to be simple data types), namely: Undefined,null,boolean, Number and string. Also contains a complex data type-object.

(1), "undefined"--not stated, or the value of the variable is undefined or uninitialized;

(2), "Boolean"--if the value of this variable is a Boolean type;
(3), "string"-the value is a string type;
(4), "number"-the value is a numeric type;
(5), "Object"--the object or value is null;
typeof This keyword is a must say, because JavaScript is loosely typed, when the variable declaration does not use the corresponding type of keyword, if you want to know the amount of basic data of a variable in the code, you can use TypeOf. It is important to note that TypeOf returns a string type.

(5), "function"--functions.

Example Validation:

1, Undefined
The undefined type has only one value, which is undefined. When the declared variable has not been initialized, the default value for the variable is undefined
function test1 () {var testmessage;alert (typeof testMessage);}
2, Null
The null type also has only one value, which is null. Null is used to denote an object that does not exist and is commonly used to indicate that a function is attempting to return an object that does not exist
function Test2 () {var testMessage = Null;alert (typeof testMessage);}

3, String
String, which can be any text in quotation marks. You can use single or double quotation marks:
function Test3 () {var testMessage = "Hello"; alert (typeof TestMessage)}
4. number
Can be a floating-point number, integer
function test4 () {var testMessage = 12;alert (typeof testMessage)}

5, Boolean
Boolean that has two values of true or false.
function Test5 () {var testMessage = True;alert (typeof testMessage)}
6, Obeject:
objects and arrays, and null as well. objects and arrays can contain different types, including objects and arrays. 
function Test6 () {var testMessage = [];alert (typeof TestMessage)}function test7 () {var testMessage = [];alert (typeof TestMessage)}function Test8 () {var testMessage = new Object (); alert (typeof TestMessage)}

7. function
function type
function Test9 () {alert (typeof Test8)}

second, value types and reference types
(1) value type: Numeric, Boolean, null, undefined
value type refers to the simple data segment stored in the stack memory, access by value, operation is the value they actually saved;
(2) Reference type: object, array, function
reference types refer to objects that are stored in the heap memory, meaning that the variables are actually saved in a pointer, which executes another location in memory, where the object is saved, the reference access, and when queried, we need to read the memory address from the stack first. And then find the value stored in the heap memory;
For example, the following are reference types
var cars=   New Array;var person= new Object;
1. Value type instance:


2. Reference type instance
   
 



Attention:
Undefined,null, empty string, 0 is equal to false, all can pass! To take the reverse.

 
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JavaScript basic data type and value type reference type description