JavaScript Lesson 1_Basic Knowledge

As the first lesson, I just want to give you a simple understanding, not too much. There are mainly three aspects:
1. Add javascript to the page
2. JavaScript data types
3. The three most basic dialog boxes of JavaScript
I think everyone knows how to add javascript, that is


/*This is also a comment,
It’s just multi-line.
*/
I don’t think I will go into detail about this today. I will leave it to the next lesson. Let’s consider it as the homework for this lesson, which is about javascript adapting to various environments. Addition of
. If the browser does not support JavaScript, what should we add to prevent the browser from displaying the JavaScript source code, etc.
The second one, which is the most important one to talk about today, is the data type of JavaScript, which mainly includes the following basic types.
String (string)
Number (number)
Boolean value (boolean)
A string is a sequence composed of a series of characters. Includes letters, numbers, and punctuation marks. Of course it can also be Chinese characters, etc. Simple
means text information.
Numbers are divided into two categories: integer numbers and floating-point numbers.
Integers include positive integers, zero and negative integers.
Numbers in JavaScript can be written using decimal, octal and hexadecimal. Here's how:
Decimal: 15 (just write the number directly)
Octal: 017 (use zero as the leading number)
Hexadecimal: 0xf (use 0x as the leading number)
Floating point numbers are also called real numbers. For convenience, they can also be expressed using scientific notation:
1.13e1, 1.5e3 (equivalent to 1.5 times 10 raised to the third power)
The numerical range of JavaScript is approximately between 10 to the power of negative 308 and 10 to the power of 308.
There is also a special numerical value NaN (not a number) in JavaScript. JavaScript uses nan to represent this meaningless result.
Boolean values: true and false. In computers, 1 is generally used to represent true, and 0 is used to represent false.
The empty value is null, which means it does not represent anything.
The undefined value is undefined, sometimes it is equal to null, sometimes there may be something wrong.
Special characters: also called escape characters. are some non-displayable special control characters starting with a backslash.
b: means backspace
n: indicates line break
Wait.
Usage of alert() method:


alert() is javascript that generates a dialog box with a confirmation button, which displays the information in brackets.
Usage of confirm() method:


confirm() is similar to alert(), the only difference is that there is an extra cancel button. Pressing OK returns true, pressing Cancel returns false.
<script> //这行是javascript脚本标记，斜杠后面的就是注释了 <br>document.write("在页面显示的javascript") //在页面显示一句话 <br></script> <script> <br>alert("在页面上显示警告对话框"); <br></script>Usage of prompt() method: <script> <br>confirm("在页面上显示确认对话框"); <br></script><script> <br>var con; <br>con=confirm("你们喜欢这样的教程吗？"); <br>if (con==true) alert("喜欢"); <br>else alert("不喜欢"); <br></script> <script> <br>var name,age; <br>name=prompt("请问您的名字？"); <br>alert(name); <br>age=prompt("多大？"); <br>alert(age); <br></script>It can not only display information, but also input information.