JS can "display" data in different ways:
(1)Writing into an alert box, using window.alert();
1 <!DOCTYPE html> 2 <html> 3 <body> 4 <h1>My first example.</h1> 5 <script> 6 window.alert(5 * 6); 7 </script> 8 </body> 9 </html>
(2)Writing into the HTML output using document.write();
1 <script> 2 document.write(5 + 8); 3 </script>
But, using document.write() after an HTML document is fully loaded, will delete all existing HTML:
<!DOCTYPE html> <html> <body> <h1>My First Web Page</h1> <p>My first paragraph.</p> <button onclick="document.write(5 + 6)">Try it</button> </body> </html>
(3)Writing into an HTML element, using innerHTML;
1 <!DOCTYPE html> 2 <html> 3 <body> 4 5 <h1>My First Web Page</h1> 6 <p>My First Paragraph.</p> 7 8 <p id="demo"></p> 9 10 <script> 11 document.getElementById("demo").innerHTML = 5 + 6; 12 </script> 13 14 </body> 15 </html>
(4)Writing into the browser console, using console.log().
1 <!DOCTYPE html> 2 <html> 3 <body> 4 5 <h1>My First Web Page</h1> 6 <p>My first paragraph.</p> 7 8 <p> 9 Activate debugging in your browser (Chrome, IE, Firefox) with F12, and select "Console" in the debugger menu. 10 </p> 11 12 <script> 13 console.log(5 + 6); 14 </script> 15 16 </body> 17 </html>
这样就可以按F12调试自己的代码了。