Data Type

JS Tutorial For TrySky IT Center (Operation and Maintenance Center)

Written by Zhang Zhihong in 2021

Data Type

JavaScript contains 7 data types: 字符串(String)、数字(Number)、布尔(Boolean)、数组(Array)、对象(Object)、空(Null)、未定义(Underfined)。

01 String

You can learn String in a example:

var myname = "JavaScript"
var language = myname + " is a scripting language."
document.write(language)

And link it in html, output is :

JavaScript is a scripting language.

Other data type’s declaration is similar.

02 Number

JS do not like other language, it’s Number type only one type, which can be a Int(integer) or Float(decimal ).

var age = 20
var length = 1.5
var z = 123e-5

In code above, you notic “123e-5”,“e” or “E” stands for ten to the e (It would be easy to understand it if you have learn C or other High-level programming languages. ). Here, “123e-5” mean “0.00123”.

03 Boolean

Boolean only two value: ture and false.

var x = ture
var y = false

04 Array

You can use Array() object to creat array.

It may be difficult to understand what is “object”, but it doesn’t matter, after learning the JAVA or other Object-oriented programming languages, you will get it. But you have not learn it , so just Remember it.

var language = new Array() /*remmember this format */
language[0] = "python"
language[1] = "JavaScript"
language[2] = "Html"
    /*maybe you want a easy way*/
var language = new Array("python", "JavaScript", "Html")
    /*or use list to creat array*/
var language = ["python", "JavaScript", "Html"]
    /*and then uses a for loop to iterate over the array to output, like in C */
for (i = 0; i < 3; i++) {
    document.write(language[i] + "</br>")
}

output :

python
JavaScript
Html

05 Object

In JavaScript, almost everything is an object.
An object is also a variable, but an object can contain multiple values (multiple variables).
In JavaScript, objects are like “containers” for variables.
Typically, JavaScript objects hold key-value pairs.
Key-value pairs are usually written as name: value (the key and value are separated by a colon).
Key-value pairs in JavaScript objects are called object properties.

在 JavaScript中，几乎所有的事物都是对象。对象也是一个变量，但对象可以包含多个值（多个变量）。
在JavaScript中，对象像是变量的“容器”。
通常，JavaScript 对象中放着键值对（键:值）。
键值对通常写法为 name : value (键与值以冒号分割)。
键值对在 JavaScript 对象通常称为对象属性。

You can declare a object like this:

var student = {
    name: "zhzhang",
    ID: "2019611000",
    age: 20,
    dorm: "JingYi"
};

Object’name is student, in this object，have name, ID, age, dorm.
You can change the value of an object’s properties by using “.” , you can get the value of an object in the same way ：

var student = {
    Name: "zhzhang",
    ID: "2019611000",
    age: 20,
    dorm: "JingYi"
};
student.dorm = "ZhiXing"
document.write(student.dorm)

Here is output:

ZhiXing

06 Null

NULL mean no value, value is empty.

07 Undefined

Undefined means the variable is declared but no value is assigned.

2021.1.14.by zhang