The alert() function in JavaScript pops up, testing techniques, and detailed explanation of how to issue alerts

In JavaScript code, you can use the alert() function of the window object to display a piece of text to debug the program, or to alert the user of relevant information:

//Use window object's alert() function
window.alert("sample text");

This The writing method can be simplified to using the alert() function directly:

//Simplified 
alert() usagealert("sample text");

If you need to display text with line breaks, you can use \n:

//Use \n in alert()
alert("The first line\nThe second line");

If you need to use tab characters, you can use \t:

//Use \t in alert()
alert("Alex\t50\t34\nBob\t59\t38");

Use of variables

In addition to displaying static strings, the alert() function can also accept variables and splice the variable value with other strings:

//Use variable in alert()
var word = "life";
alert("The magic word is: " + word + ". Don't panic.");

Unfortunately, although the alert() function can accept variables, it can only do this string concatenation operation; contrary to another debugging method console.log(), alert() The function does not accept passing parameters as strings. Take the following code as an example:

//Try to use parameter in alert(), will fail
var name = "Bob";
var years = 42;
alert("%s is %d years old.", name, years);

If the alert() function accepts a string parameter, the expected output result will be "Bob is 42 years old."; but in fact the alert() function does not This is supported, so the final output is "%s is %d years old."

Pop-up window style

Because the pop-up box used by the alert() function is a browser system object rather than a web page document object, it cannot be passed in the alert() function Use HTML tags to define the style of the pop-up box - the HTML tags will be displayed intact. For the following code:

//Try to use HTML tags in alert(), will fail
alert("<b>Test Text</b>");

The output result is not bold "Test Text".

If you really need to change the style of the alert box, you can have the following two options:

1. Use Unicode characters in the alert() function. The advantage of this solution is that it is very simple to implement, but its limitations are also obvious: the expressive power of Unicode characters is very limited.

2. Instead of using the alert() function, use HTML components to simulate pop-up boxes (such as using jQuery UI Dialog). The advantage of this solution is that the pop-up box will be very expressive, but its use will increase the complexity of the front-end code.

alert() function can be used to alert users with information and can also be used to debug programs. For the former, using components such as jQuery UI Dialog can greatly increase expressiveness and user experience; for the latter, since the alert() pop-up box will block the execution of JavaScript code, in many cases, console.log() is used to Debugging the program is a better solution.

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