The usage of radio buttons in JavaScript is similar to that of check boxes. The difference lies in the application in HTML. A checkbox is a switch. If a checkbox is selected, you can click it again to deselect it. But if a radio button is selected, you can only deselect it by selecting another radio button. Example:
In this example, if you want to deselect a radio button, you must click on another radio button. Look at the following program again:
When the first radio button box is selected, the function offButton() is called . The function is as follows:
function offButton()
{
var the_box = window.document.form_1.radio_1;
if (the_box.checked == true)
{
window.document.form_1.radio_2.checked = false;
This example is very similar to the previous checkbox example. The main difference is this line:
window.document.form_1.radio_2.checked = false;
This line Directive instructs JavaScript to close another button when this button is clicked. Since the function of another button is very similar to this one:
function onButton()
{var the_box = window.document.form_1.radio_2;
if (the_box.checked == true)
{
window.document.form_1.radio_1.checked = false; }
Menu is the most peculiar form option we have learned. There are two basic formats: following menus and list menus. The following is an example:
< ;option>spider
;
>
Note that the name of this menu is pulldown_1, but each option has no name. So it's a bit difficult to call each of the options.
Fortunately, arrays can help us call the options. If you want to change the second option in the following menu, you can do this:
window.document.form_1.pulldown_1.options[1].text = 'new_text';
This is because the menu element has an options attribute, which is an array of all options in the menu. Click change the selectt and then use the drop-down menu to see if its selection has been changed. Now the 2nd option should be *thau*.
In addition to the option attribute, the menu also has an attribute called selectedIndex. After an option is selected, the selectedIndex attribute will become the array index number (serial number) of the selected option. Select an option in the second list menu and check the index number. Remember that the first option in the array has index 0.
The name of the form is form_1, and the name of the list menu is list_1. The selectedIndex attribute value is window.document.form_1.list_1.selectedIndex. You can also
set the selectedIndex as follows: window.document.form_1.list_1.selectedIndex = 1; and highlight the second option. Once you get the index number of the selected item, you can find its content:
var the_select = window.document.form_1.list_1;
var the_index = the_select. selectedIndex;
var the_selected = the_select.options[the_index].text;
The selectedIndex attribute is useful, but what happens if multiple options are selected at the same time?
The handler of the menu element is onChange(). When the menu changes, the processor is activated.
Try this example and read the comments below:
My favorite animal is...
Comment a relatively complex JavaScript program. First, let’s look at the form itself:

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.


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