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js basic entry function

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Mar 31, 2018 am 11:42 AM

javascriptgetting Startedfunction

This article introduces you to the basic introductory functions of js. It is more detailed and basic. Friends in need can take a look

1: Function method :

Function: Encapsulate a piece of code! This code implements a certain function. When this function is needed, the function is called.

java：

Modifier return type method name (Data type variable name, multiple) {

Method body;

1.1 The first way to define a function:

js
function function name (parameter list) {

Function body;

｝

Function details:

1. The function must be executed after being called.

2. If the function has a return value, you can directly use the data returned by return in the function body. Functions in JS do not have the restriction of return value type.

3. If the function needs to receive parameters, write the variable name directly without the var keyword.
4. There is no concept of function overloading in JS. If there are multiple functions with the same name in JS, the previous functions will be overwritten.

5. In JS, if a function needs to accept parameters but does not pass them, then the variables are all undefined

6. Regardless of whether the function in JS accepts parameters or not, when we call it, Parameters can be passed to it.

7. There is a built-in array (arguments) parameter in the function in JS to receive all the data passed. Using arguments, this parameter is actually an array object itself.

Note: If you use a function in JS later and need to accept parameters, define the variables on the function. If not, do not define them. Arguments array operations are rarely used.
<script type="text/javascript">
		//定一个函数----求和
		//1.在js中，参数列表中，不能书写var 。 如果一个函数需要参数，直接去定义一个参数的名字就可以了
		//2.函数，一定要被调用才可以去执行。 调用的方式： 函数名(); 
		//3.如果函数需要返回值，直接在函数中去书写return;
		//4.在js中没有重载的概念的。如果函数名相同，后面的会把前面的进行覆盖。
		/* function sum(a , b ){
			alert(a+b);
		}
		 	sum(2,3);//方法不调用，不执行
		 	 */
// 	======================================================	 	 
		 /* function sum(a , b ){
		 		return a+b;
		 	}
		 	var s = sum(2,5) ; // 如果需要返回值，就直接return 	
		 	alert(s); */
// =============================================================		 	
		 	function sum(a , b ){
		 		alert(1);
		 		return a+b ;
		 	}
		 	
			function sum(a , b ,c ){  //js中没有重载的含义，如果方法名相同，那么后面的会把前面的覆盖
		 		alert(2);
		 		return a+b ;
		 	}
		 	
		 	var s = sum(2,4);//按java来说两个参数应该会去调两个参数的
		 	alert(s);
	</script>

Bind a method:

1.2 The second definition method of function:

Writing method: var function Name = new Function("Parameter list", "Function body");

The first parameter represents the parameter list

The second parameter represents the function body.

#The function list and parameter body are both defined as strings.

Writing functions are too complicated, so developers rarely use them

1.3 The third way to define a function: anonymous function:

Writing method:

function（参数列表）｛

函数体；

｝

事件：可以理解为一些行为或者动作。如果该行为或者动作有意义，需要我们去做一些事情，此时可以通过事件去调用js中的函数，实现某些功能。

<html>
  <head>
    <title>18函数的第三种定义方式.html</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
	<script type="text/javascript">
		/*  
			1、页面的加载顺序
			2、事件： 一个动作或者是一个操作。
			3、window.onload === 表示 页面加载完毕 会触发
			4、如何为事件去绑定一个函数   对象.事件名=function(){}
		*/
	
	/* // 此时相当于给函数一个名字，demo
	   var demo = function(){
			alert("demo");
		}
		//正常的方式函数名（）去调用
	   demo(); */
	  // window.onload 表示一个事件。 表示当前的页面全部加载完成。
	  /*  
	  		考虑js的执行顺序。或者html的页面的加载顺序。
	  		浏览器加载页面的时候，从上向下，逐步的去加载
	  */
	  // 事件： 理解为一件事，或这是一个动作。 例如按钮，点击的时候。
	  
	  alert("window.onload 之前");
	  	// 函数的第三中定义方式，通常与一个事件进行绑定使用。
	  window.onload =  function(){
		alert("demo");
     	  		// 1、把按钮的标签获取到 --document.getElementById根据标签的id的属性，获取当前标签
		  var _button = document.getElementById("b1");
		  // 对象.事件名 = function(){}
		  _button.onclick = function(){
		  		alert("您点击了按钮");
		  }

	  }
	</script>
  </head>
  
  <body>
  	<h1 id="这是h">这是h1</h1>
  	<input type="button" id="b1" value="按钮">
  </body>
</html>

1.4全局函数：

js为我们提供了几个全局函数。我们可以直接使用的函数。

url：统一资源定位符

http://www.baidu.com/s/fasdf/basdf

http:// 协议：

www 万维网。主机名

.baidu.com 域名

/s/fasdf/basdf ---- 资源路径。（资源：互联网中存在的一些文件或者是程序。例如：html页面。图片，视频，音频。。。。）

uri：统一资源标识符

/s/fasdf/basdf uri实际上就是一个资源路径。

url 是一种具体的uri 。所以uri的表示范围大于url。(相对来说)

uri 的编码。浏览的地址栏中的内容，会提交到一个服务器。涉及到http协议。不支持中文在url的存在。需要进行uri的编码。

相关推荐：

掌握js函数

进一步了解js函数

js函数和变量的提升及闭包讲解

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