What is the usage of alert in javascript-JS Tutorial-php.cn

What is the usage of alert in javascript

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Release： 2021-06-15 11:02:21

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In JavaScript, the usage of alert is "alert (plain text displayed in the dialog box)". The alert method is used to display an alert box with a specified message and an OK button. It can be used to alert the user or debug the program.

What is the usage of alert in javascript

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

alert() method is used to display an alert box with a specified message and an OK button.

Syntax

alert(message)

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message refers to the plain text (not HTML text) to be displayed in the dialog box that pops up on the window

Example:

<html>
<head>
<script type="text/javascript">
function disp_alert()
{
alert("我是一个消息框！")
}
</script>
</head>
<body>

<input type="button" onclick="disp_alert()" value="显示消息框" />

</body>
</html>

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Alert in JS is used to pop up a warning box in the browser.

There are three ways to use alert. Different ways have different effects.

The first way: write directly in the script tag

The code is as follows:

<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<script type="text/javascript">
			alert("这是一个警告框");
		</script>
	</head>
	<body>
		 <p>你看我出不出来</p>；
	</body>
</html>

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The effect is as follows:

What is the usage of alert in javascript

##As can be seen from the renderings, the p tag that was supposed to be executed was not executed.

This is because when alert is used in this method, the code after the alert will not be executed initially. Only after the warning box is closed, the following content will be executed.

This method is the simplest, but because it cannot execute the code after the alert at the same time, it affects the user's perception, so it is not recommended.

The second way: write inside a certain tag in the body

The code is as follows:

<body>
		<!--将alert编写到onclick属性中，单击后，会弹出警告框-->
		 <button onclick="alert(&#39;点，点什么点&#39;)">你点我一下</button><br /><br />
		 	
		 <!--将alert写在超链接的href属性中，点击超链接，会弹出警告框-->
		 <a href="javascript:alert(&#39;叫你别点，你非要点&#39;)">别点我</a><br />
		 
		  <p>你看我出不出来</p>
	</body>

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The implementation effect diagram is as follows:

What is the usage of alert in javascript

Using this method, there will not be the problem of the first method, but with this method, alert may appear in many places on a page.

It is inconvenient to maintain and also Not recommended.

The third way: use external alert

The external alert code is as follows:

alert("这是外部alert");
//重新创建一个js文件，专门用于写alert

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The code referencing the external alert is as follows:

<script type="text/javascript" src="alert.js">
		/*加入src="路径"，可以引入外部alert*/
			alert("这是一个警告框");
		</script>

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The implementation effect diagram is as follows ：

What is the usage of alert in javascript

Using this method, you need to remember the path of the external alert in order to reference it

It is best to write it in the same folder.

This method will not cause the problems of the first method, will not affect the user's perception, and is easy to maintain.

But after using this method, the internal alert under the scrip tag cannot be After execution, you can only rewrite a script

This method is recommended.

[Recommended learning:

javascript advanced tutorial]

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