Things to note when using alert() in JavaScript

In our previous article, we introduced the use of alert() in JavaScript and modified the style of alert(). I believe everyone is familiar with the alert() method and should have used it to reflect Some values ​​in operation. Today I will introduce to you what you need to pay attention to when using alert() in JavaScript! The

alert() method is used to display an alert box with a specified message and an OK button.
Syntax: alert(message)
message represents the plain text (not HTML text) to be displayed in the pop-up dialog box on the window.

alert() is a destructive method. When executed, the code after the pop-up window will not be executed.

Alert() also has the disadvantage that it converts the parameter message into a string.
If we determine that the parameter message is a string when using it, we can use it with confidence, but if not, we should be careful, as follows:

alert([1,2,3]); //弹出的对话框中显示的是1,2,3

In this case, it is still possible Okay, at least we know that the parameter is an array and the content is 1, 2, 3, but the following situation is worse:

<p style="margin-bottom: 7px;">alert([1,2,3,[4,5,6]]); //弹出的对话框中显示的是1,2,3,4,5,6<br/></p>

We can't judge the parameters at all based on what is displayed in the pop-up dialog box It is an array nested within an array. The relationship between the output 1,2,3,4,5,6 and [1,2,3,[4,5,6]] seems to be:

String([1,2,3,[4,5,6]]); //输出的结果是1,2,3,4,5,6
String([1,2,3]); //输出的结果是1,2,3

When using alert(), will the parameter message be first called the String() method to convert the message into a string?

Let’s continue reading:

alert({x:1,y:2});//输出的结果是[object Object]
String(({x:1,y:2}));//输出的结果也是[object Object]
alert("abc");//输出的结果是abcString("abc");//输出的结果是abc
alert(123);//输出的结果是123String(123);//输出的结果是123
typeof(String(({x:1,y:2}))); //输出结果是string
typeof(String([1,2,3,[4,5,6]])); //输出结果是string
typeof(String("abc")); //输出结果是string
typeof(String(123)); //输出结果是string

Summary:

After reading this, we will understand clearly. When alert(), String() will first be called to force the parameter message to a string, and then the string will be displayed in the pop-up dialog box. Therefore, the text displayed in the dialog box popped up by alert() and the parameter message are sometimes different.

Related recommendations:

Introduction to the method of modifying the alert style in JavaScript

Instructions for using alert() in JavaScript

##The difference between alert() and console.log() in javascript

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