JavaScript Beginner Tutorial (Lesson 5)_Basic Knowledge
Now you know the basics of computer programming. Let's continue to study the Document Object Model (Document Object Model-DOM). The click relationship of the DOM starts with the window object being a Document object in each window object. We'll focus on the Document object and see how you can use it to obtain information from your users and dynamically display new information.
We have already seen an attribute of the file object - the Images array. In Lesson 3, the first image in the file can be modified by changing its src attribute.
Example:
window.document.images[0].src='some_new_picture.gif';
This command will change the first image in the document into a new image named some_new_picture.gif. In the DOM, each image in the image array is also an object. So the images[0].src instruction works like an object. It means: call the object image[0] in Image from the Image array and set its src attribute. To translate it: call the document attribute from the window, call the first image from the image array of the document, and set its src attribute to the image some_new_picture.gif.
The Image object has many other interesting properties. For example, you can let JavaScript check whether an image has been fully loaded before doing other things. However, we can only talk about these properties in future lessons. Today, we’re going to talk about feedback forms and how to use them in JavaScript.
The feedback form is part of the HTML 1.0 specification. Many people don't know much about it. Many people only think that it is only possible due to client-side CGI programming. In fact, even if you are not a CGI programmer, feedback forms provide you with a lot of functionality. JavaScript can be used to add various functionality to feedback forms. And it does not require the assistance of client CGI.
If you don’t understand how feedback forms work, please take the relevant courses in Introduction to HTML. Then start studying this lesson.
First of all, in javascript, the feedback form is also stored in an object array. You can call the first image in the image array through window.document.images[0], and you can also call the first form in the feedback form array using window.document.forms[0]. You can name the image and similarly name the feedback form. For example, if the feedback form
is programmed as follows:
You can reference the form in one of the following two ways:
var the_form = window.document.forms[0];
var the_same_form = window.document.first_form;
More often, you need to reference elements within the form, For example, the text field in the example above.
Slide your mouse over the link to see what happens.
Yes, and I know it. No!
This wonderful transformation can be achieved by changing the value of the text field.
Change the link of the text field to:
It means that the form calls the first form and sets its value to 'Clap clap!' The second line has a similar effect. This is very similar to changing the src of an image. It's just that the text field changes the value.
A similar method can be used to change the value of textareas:
Part 1 Part 2
Form code: