Write your first JavaScript program

When learning a new language, everyone likes to use "hello world" as the first program, so now we write a JavaScript version:

The JavaScript code is placed in tag, the effect of this code is to pop up a small box that displays "hello world!". Save this code as an HTML file, name it "test.html", then double-click the file, the system will call the FireFox browser to open it:

Visible writing JavaScript program It is very convenient.