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This article mainly introduces the relevant knowledge of what the commonly used data types of javascript are, the content is detailed and easy to understand, the operation is simple and fast, and has a certain reference value, I believe you will have something to gain after reading this javascript commonly used data types, let's take a look at it.

Javascript commonly used data types are: 1, null type, which represents a null value, defines a null object pointer; 2, undefined type, represents an undefined value; 3, number type; 4, string type; 5, boolean type; 6, object type; 7, Array type.

The operating environment of this tutorial: windows7 system, javascript1.8.5 version, Dell G3 computer.

Data types commonly used in javascript

The data type description null null value, represents the non-object undefined undefined value, represents the unassigned initialization value number number, the mathematical operation value string string, represents the information flow boolean Boolean value, the logical operation value object object, represents the compound structure data set Array array, contains the ordered set of encoded values.

1 、 Null

The Null type has only one value, null, which represents a null value and defines a null object pointer.

Use the typeof operator to detect the null value and return Object, indicating that it is an object type, but JavaScript classifies it as a special class of values.

By setting the initialization value of the variable to null, you can define an alternate empty object, that is, a special object value, or non-object. For example, if you detect that an object is empty, you can initialize it.

If (men = = null) {men = {/ / initialize men}}

2. Undefined type

Undefined is the only value of type Undefined, which represents an undefined value. The default value is undefined when the declaration variable is not assigned, or when the definition property is not set.

Example 1

Undefined is derived from null,null and undefined, which both represent vacant values, are false when converted to Boolean values, and can be equal.

Console.log (null = = undefined); / / returns true

Null and undefined are of two different types and can be detected using the congruence operator (= =) or the typeof operator.

Console.log (null = undefined); / / falseconsole.log (typeof null); / / return "object" console.log (typeof undefined); / / return "undefined"

Example 2

To detect whether a variable is initialized, you can use undefined to quickly detect it.

Var a; / declare the variable console.log (a); / / return the default value of the variable is undefined (a = = undefined) & (a = 0); / / detect whether the variable is initialized, otherwise assign it a value of console.log (a); / / return the initial value of 0

You can also use the typeof operator to detect whether the variable is of type undefined.

(typeof a = = "undefined") & & (a = 0); / / detect whether the variable is initialized, otherwise assign a value to it

3. Boolean type

Boolean (Boolean) contains only two fixed values: true and false. Where true stands for "true" and false for "false".

In JavaScript, six special values, undefined, null, "", 0, NaN, and false, are false when converted to Boolean values, which are called false values. Any type of data other than a false value is true when converted to a Boolean value.

Example

Use the Boolean () function to cast a value to a Boolean value.

Console.log (Boolean (0)); / / return falseconsole.log (Boolean (NaN)); / / return falseconsole.log (Boolean (null)); / / return falseconsole.log (Boolean ("")); / / return falseconsole.log (Boolean (undefined)); / / return false

4 、 Number:

There are two forms of representation of this type, the first is an integer and the second is a floating point number. Integers: can be represented by decimal, octal, and hexadecimal literal values. Floating point: this value must contain a decimal point and must be followed by a decimal point.

5 、 String:

The String type is used to represent a sequence of zero or more 16-bit Unicode characters, that is, strings. As for using single quotation marks or double quotation marks, there is no difference in js. Remember to show up in pairs.

6 、 Object:

The Object data type, called an object, is a collection of data and functions. You can create it with the new operator followed by the name of the object type you want to create. It can also be created in literal notation. Add an attribute with a different name (any string including an empty string) to it.

7 、 Array

The JavaScript array is written in square brackets. The items of the array are separated by commas.

The following code declares (creates) an array named cars that contains three items (car brands):

Var cars = ["Porsche", "Volvo", "BMW"]

The array index is based on zero, which means that the first item is [0], the second item is [1], and so on.

Arrays in ECMAScript are quite different from arrays in other languages:

Each item of the ECMAScript array can hold any type of data

The size of the ECMAScript array can be adjusted dynamically, adding or deleting elements to the array.

This is the end of the article on "what are the common data types in javascript?" Thank you for reading! I believe that everyone has a certain understanding of the knowledge of "what data types are commonly used in javascript". If you want to learn more knowledge, you are welcome to follow the industry information channel.

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