1, JavaScript code blocks
JavaScript can be combined in batches.
Code block starts with a left curly brace and ends with the closing brace.
Action code block is a sequence of statements executed collectively.
<body>
<h1>我的 Web 页面</h1>
<p id="myPar">我是一个段落。</p>
<div id="myDiv">我是一个div。</div>
<p>
<button type="button" onclick="myFunction()">点击这里</button>
</p>
<script>
function myFunction(){
document.getElementById("myPar").innerHTML="你好世界！";
document.getElementById("myDiv").innerHTML="你最近怎么样?";
}
</script>
<p>当您点击上面的按钮时，两个元素会改变。</p>
</body>
2, single-line comments begin with //.
// 输出标题：
document.getElementById("myH1").innerHTML="欢迎来到我的主页";
// 输出段落：
document.getElementById("myP").innerHTML="这是我的第一个段落。";
3, JavaScript multi-line comments
多行注释以 /* 开始，以 */ 结尾。
/*
下面的这些代码会输出
一个标题和一个段落
并将代表主页的开始
*/
document.getElementById("myH1").innerHTML="欢迎来到我的主页";
document.getElementById("myP").innerHTML="这是我的第一个段落。";
4, JavaScript variables
<script>
var x=5;
var y=6;
var z=x+y;
document.write(x + "<br>");
document.write(y + "<br>");
document.write(z + "<br>");
</script>
5, variable - naming rules
变量必须以字母开头
变量也能以 $ 和 _ 符号开头（不过我们不推荐这么做）
变量名称对大小写敏感（y 和 Y 是不同的变量）
6, a statement, a number of variables
You can declare many variables in a statement. Var statement to the beginning, are separated by commas variable to:
var = LastName "Doe", Age = 30, Job = "Carpenter";
Acknowledgment may span multiple lines:
var = LastName "Doe",
Age = 30,
Job = "Carpenter";
A plurality of values may not assign the same statement declared:
var X, Y, Z =. 1;
x, y is undefined, z is 1.
7、Value = undefined
In a computer program, often declare variables without value. Not used to declare a variable value, and its value is actually undefined.
After executed the following statement, the value of the variable carname will be undefined:
var carname;
8, JavaScript Data Types
值类型(基本类型)：字符串（String）、数字(Number)、布尔(Boolean)、对空（Null）、未定义（Undefined）、Symbol。
引用数据类型：对象(Object)、数组(Array)、函数(Function)。
9, JavaScript has a dynamic type
JavaScript has a dynamic type. This means that the same variables can be used as different types:
Examples
var x; // x 为 undefined
var x = 5; // 现在 x 为数字
var x = "John"; // 现在 x 为字符串
10, JavaScript string
The character string is stored (such as "Bill Gates") variables.
It may be any text string in quotation marks. You can use single or double quotes:
Examples
var carname="Volvo XC60";
var carname='Volvo XC60';
11, JavaScript digital
JavaScript is only one digital type. With decimal number can also be without:
Example
var x1=34.00; //使用小数点来写
var x2=34; //不使用小数点来写
12, JavaScript Boolean
Boolean (logic) can have only two values: true or false.
to true X = var;
var Y = to false;
13, JavaScript arrays
The following code creates an array of cars named:
var = new new cars the Array ();
cars [0] = "Saab";
cars [. 1] = "Volvo";
cars [2] = "the BMW";
或者 (condensed array):
var cars=new Array(“Saab”,“Volvo”,“BMW”);
Or (literal array):
Example
var cars = [ "Saab", "Volvo", "BMW"];
14, JavaScript objects
Objects are separated by braces. Within brackets, the name and attribute of the object in the form of value pairs (name: value) is defined. Properties are separated by commas:
var Person = {FirstName: "John", LastName: "Doe", ID: 5566};
Examples of the above objects (Person) has three attributes: firstname, lastname, and id.
Spaces and wrap irrelevant. Statement may span multiple lines:
var Person = {
FirstName: "John",
LastName: "Doe",
ID: 5566
};
Object Properties There are two addressing modes:
Example
name = person.lastname;
name = Person [ "LastName"];
15、Undefined 和 Null
Undefined variable does not contain this value represents the value.
By setting the value of the variable to null to clear variable.
Examples of
cars = null;
Person = null;
16, declare a variable type
When you declare a new variable, you can use the keyword "new" to declare its type:
var = new new String carname;
var = new new the X-Number The;
var = the y-new new Boolean;
var cars = new new Array;
var the Person = new new Object;
17, JavaScript objects
JavaScript object is to have the properties and methods of data.
18, access to object properties
You can access the object properties in two ways:
Example. 1
person.lastName;
Example 2
Person [ "lastName"];
19, object methods
The method defines a function object, and stored as attributes of the object.
By adding object method calls () (as a function).
The person object instance visited the fullName () method:
Example
name = person.fullName ();
20, access to the object method
You can use the following syntax to create an object method:
methodName: function () {} code Lines
You can use the following syntax to access object methods:
objectName.methodName ()
Typically the fullName () method as a person object, fullName as an attribute.
There are several ways to create, use and modify the JavaScript objects.