Basic data types for js basic improvement learning

This time I will bring you the basics of js basic improvement learning Data types, what are the precautions when using js basic data types, the following is a practical case, let’s take a look .

The data types of JavaScript are divided into two major types:

1. Basic data types:

String (String)

Number (Number):

Boolean: true, false

undefined: undefined

null: empty

NaN: not a number (isNaN( 10), returns false, indicating whether it is a number. If you pass a number, an error will be reported)

2. Reference data type (object/conforming data type):

Inherit Object

An object in js is a collection of properties and methods. Here we talk about reference types. Reference types are a data structure used to organize data and functions together. Reference types are sometimes called object definitions because they describe the properties and methods that a type of object has.

Basic data type:

In the first JS, we found the conversion, how to convert it specifically? What are the order and rules? Explain:

Reason for conversion: python and javascript are weak data-type languages, so they will be converted

Priority level: string >float >int > boolean

A simple example:

1. The priority of strings is higher than numbers. Numbers will be converted into strings and can be output.

2. The floating point type is higher than the integer type, and the output is 12.3

3. The isNaN method is used to determine if it is not a number

For example, is it a number?

Yes, so the result is Flese

type of   123　　 //Number
type of   'abc'　　//String
type of    true       //Boolean
type of    undefined   //Undefined
type of    null        //Object
type of    { }           //Object
type of    [ ]           //Object
type of    console.log()       //Function

1.Number type

The Number type contains two types of values: integers and floating point numbers (floating point numbers must contain a decimal point, and there is at least one digit after the decimal point).

NaN: non-numeric type. Features: ① Any operation involving NaN will return NaN ② NaN is not equal to itself.

isNaN() function is used to check whether its argument is a non-numeric value.

isNaN(123)  //false   isNaN("hello")  //true

2.String type

String has length attribute.

String conversion: Transformation function String(), suitable for any data type (null, undefined converted to null and undefined);

toString() method (null, defined without toString( )method).

3.Boolean type

This type has only two values, true and false

4.Undefined type

has only one value, the undefined value. If a variable is declared using var, but the variable is not initialized, the value of the variable is undefined.

5.Null type

The null type is regarded as a null object pointer. As mentioned above, the null type is also a null object reference.

6.Object type

Object in js is a collection of properties and methods. Here we talk about reference types. Reference types are a data structure used to organize data and functions together. Reference types are sometimes called object definitions because they describe the properties and methods of a class of objects.

Three major reference types:

1.Object type

Most of the type values ​​we see are instances of the Object type. There are two ways to create Object instances. .

The first way is to use the new operator followed by the Object

, as shown below

var person = new Object();
person.name = "Micheal";
person.age = 24;

var person = {
　　name : "Micheal",
　　age : 24
};

2.Array type

Each item of the array can be used to save any type of data, that is to say, the first position of the array can be used to save the string, and the second The first position stores the value, and the third position stores the object.... In addition, the size of the array can be dynamically adjusted.

There are two basic ways to create an array

The first is to use the Array constructor, as shown below

var colors = new Array("red","blue","yellow");

The second is to use the array literal representation, As shown below

var colors = ["red","blue","yellow"];

3 Function type

Each function is an instance of the Function type, and has the same properties and methods as other reference types. Functions are usually

declaration syntax, as shown below

function sum(num1,num2){
　　return num1 + num2;
};

are used to define functions.

var sun = function (){
　　return sum1 + sum2;
};

也就是说，js按照存储方式分为值类型和引用类型。那么他们的计算有什么区别呢？

题目1：

var a = 100;
　　　　var b = a;
　　　   a = 200;
　　　　console.log (b);

题目2：

var a = {age : 20};
　　　　var b = a;
　　　　b.age = 21;
　　　　console.log (a.age);

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