오래된 라디오의 버튼과 비슷한 형태와 동작 방식을 가졌기에 라디오 버튼이라고 부릅니다.
radio 유형의 {{htmlelement("input")}} 요소는 보통 서로 관련된 옵션을 나타내는 라디오 버튼 콜렉션, 라디오 그룹에 사용합니다. 임의의 그룹 내에서는 동시에 하나의 라디오 버튼만 선택할 수 있습니다. 라디오 버튼은 흔히 원형으로 그려지며, 선택한 경우 속을 채우거나 강조 표시를 합니다.
오래된 라디오의 버튼과 비슷한 형태와 동작 방식을 가졌기에 라디오 버튼이라고 부릅니다.
참고: 체크박스도 라디오 버튼과 비슷하지만 중요한 차이점이 하나 있습니다. 라디오 버튼은 여러 값에서 단 하나만 선택할 때 사용하지만, 체크박스는 각각의 값을 켜고 끌 수 있다는 점입니다. 다수의 컨트롤이 존재할 때 라디오 버튼은 전체에서 하나를 허용하고, 체크박스는 여러 개 선택을 허용합니다.
| {{anch("값")}} | 라디오 버튼의 값을 나타내는 {{domxref("DOMString")}}. |
| 이벤트 | {{event("change")}}, {{event("input")}} |
| 지원하는 공통 특성 | checked, value |
| IDL 특성 | {{anch("checked")}}, {{anch("value")}} |
| 메서드 | {{domxref("HTMLInputElement.select", "select()")}} |
The value attribute is a {{domxref("DOMString")}} containing the radio button's value. The value is never shown to the user by their {{Glossary("user agent")}}. Instead, it's used to identify which radio button in a group is selected.
A radio group is defined by giving each of radio buttons in the group the same {{htmlattrxref("name", "input")}}. Once a radio group is established, selecting any radio button in that group automatically deselects any currently-selected radio button in the same group.
You can have as many radio groups on a page as you like, as long as each has its own unique name.
For example, if your form needs to ask the user for their preferred contact method, you might create three radio buttons, each with the name property set to contact but one with the {{htmlattrxref("value", "input")}} email, one with the value phone, and one with the value mail. The user never sees the value or the name (unless you expressly add code to display it).
The resulting HTML looks like this:
<form>
<p>Please select your preferred contact method:</p>
<div>
<input type="radio" id="contactChoice1"
name="contact" value="email">
<label for="contactChoice1">Email</label>
<input type="radio" id="contactChoice2"
name="contact" value="phone">
<label for="contactChoice2">Phone</label>
<input type="radio" id="contactChoice3"
name="contact" value="mail">
<label for="contactChoice3">Mail</label>
</div>
<div>
<button type="submit">Submit</button>
</div>
</form>
Here you see the three radio buttons, each with the name set to contact and each with a unique value that uniquely identifies that individual radio button within the group. They each also have a unique {{domxref("Element.id", "id")}}, which is used by the {{HTMLElement("label")}} element's {{htmlattrxref("for", "label")}} attribute to associate the labels with the radio buttons.
You can try out this example here:
{{EmbedLiveSample('Defining_a_radio_group', 600, 130)}}
When the above form is submitted with a radio button selected, the form's data includes an entry in the form contact=value. For example, if the user clicks on the "Phone" radio button then submits the form, the form's data will include the line contact=phone.
If you omit the value attribute in the HTML, the submitted form data assigns the value on to the group. In this scenario, if the user clicked on the "Phone" option and submitted the form, the resulting form data would be contact=on, which isn't helpful. So don't forget to set your value attributes!
Note: If no radio button is selected when the form is submitted, the radio group is not included in the submitted form data at all, since there is no value to report.
It's fairly uncommon to actually want to allow the form to be submitted without any of the radio buttons in a group selected, so it is usually wise to have one default to the checked state. See {{anch("Selecting a radio button by default")}} below.
Let's add a little bit of code to our example so we can examine the data generated by this form. The HTML is revised to add a {{HTMLElement("pre")}} block to output the form data into:
<form>
<p>Please select your preferred contact method:</p>
<div>
<input type="radio" id="contactChoice1"
name="contact" value="email">
<label for="contactChoice1">Email</label>
<input type="radio" id="contactChoice2"
name="contact" value="phone">
<label for="contactChoice2">Phone</label>
<input type="radio" id="contactChoice3"
name="contact" value="mail">
<label for="contactChoice3">Mail</label>
</div>
<div>
<button type="submit">Submit</button>
</div>
</form>
<pre id="log">
</pre>
Then we add some JavaScript to set up an event listener on the {{domxref("HTMLFormElement/submit_event", "submit")}} event, which is sent when the user clicks the "Submit" button:
var form = document.querySelector("form");
var log = document.querySelector("#log");
form.addEventListener("submit", function(event) {
var data = new FormData(form);
var output = "";
for (const entry of data) {
output = output + entry[0] + "=" + entry[1] + "\r";
};
log.innerText = output;
event.preventDefault();
}, false);
Try this example out and see how there's never more than one result for the contact group.
{{EmbedLiveSample("Data_representation_of_a_radio_group", 600, 130)}}
In addition to the common attributes shared by all {{HTMLElement("input")}} elements, radio inputs support the following attributes:
| Attribute | Description |
|---|---|
{{anch("checked")}} |
A Boolean indicating whether or not this radio button is the currently-selected item in the group |
{{anch("value")}} |
The string to use as the value of the radio when submitting the form, if the radio is currently toggled on |
A Boolean attribute which, if present, indicates that this radio button is the currently selected one in the group.
Unlike other browsers, Firefox by default persists the dynamic checked state of an <input> across page loads. Use the {{htmlattrxref("autocomplete","input")}} attribute to control this feature.
The value attribute is one which all {{HTMLElement("input")}}s share; however, it serves a special purpose for inputs of type radio: when a form is submitted, only radio buttons which are currently checked are submitted to the server, and the reported value is the value of the value attribute. If the value is not otherwise specified, it is the string on by default. This is demonstrated in the section {{anch("Value")}} above.
We already covered the fundamentals of radio buttons above. Let's now look at the other common radio-button-related features and techniques you may need to know about.
To make a radio button selected by default, you simply include checked attribute, as shown in this revised version of the previous example:
<form>
<p>Please select your preferred contact method:</p>
<div>
<input type="radio" id="contactChoice1"
name="contact" value="email" checked>
<label for="contactChoice1">Email</label>
<input type="radio" id="contactChoice2"
name="contact" value="phone">
<label for="contactChoice2">Phone</label>
<input type="radio" id="contactChoice3"
name="contact" value="mail">
<label for="contactChoice3">Mail</label>
</div>
<div>
<button type="submit">Submit</button>
</div>
</form>
{{EmbedLiveSample('기본_선택_항목_지정하기', 600, 130)}}
In this case, the first radio button is now selected by default.
Note: If you put the checked attribute on more than one radio button, later instances will override earlier ones; that is, the last checked radio button will be the one that is selected. This is because only one radio button in a group can ever be selected at once, and the user agent automatically deselects others each time a new one is marked as checked.
In the above examples, you may have noticed that you can select a radio button by clicking on its associated {{htmlelement("label")}} element, as well as on the radio button itself. This is a really useful feature of HTML form labels that makes it easier for users to click the option they want, especially on small-screen devices like smartphones.
Beyond accessibility, this is another good reason to properly set up <label> elements on your forms.
Radio buttons don't participate in constraint validation; they have no real value to be constrained.
The following example shows a slightly more thorough version of the example we've seen throughout the article, with some additional styling, and with better semantics established through use of specialized elements. The HTML looks like this:
<form>
<fieldset>
<legend>Please select your preferred contact method:</legend>
<div>
<input type="radio" id="contactChoice1"
name="contact" value="email" checked>
<label for="contactChoice1">Email</label>
<input type="radio" id="contactChoice2"
name="contact" value="phone">
<label for="contactChoice2">Phone</label>
<input type="radio" id="contactChoice3"
name="contact" value="mail">
<label for="contactChoice3">Mail</label>
</div>
<div>
<button type="submit">Submit</button>
</div>
</fieldset>
</form>
There's not much new to note here except for the addition of {{htmlelement("fieldset")}} and {{htmlelement("legend")}} elements, which help to group the functionality nicely and in a semantic way.
The CSS involved is a bit more significant:
html {
font-family: sans-serif;
}
div:first-of-type {
display: flex;
align-items: flex-start;
margin-bottom: 5px;
}
label {
margin-right: 15px;
line-height: 32px;
}
input {
-webkit-appearance: none;
-moz-appearance: none;
appearance: none;
border-radius: 50%;
width: 16px;
height: 16px;
border: 2px solid #999;
transition: 0.2s all linear;
margin-right: 5px;
position: relative;
top: 4px;
}
input:checked {
border: 6px solid black;
}
button,
legend {
color: white;
background-color: black;
padding: 5px 10px;
border-radius: 0;
border: 0;
font-size: 14px;
}
button:hover,
button:focus {
color: #999;
}
button:active {
background-color: white;
color: black;
outline: 1px solid black;
}
Most notable here is the use of the {{cssxref("-moz-appearance")}} property (with prefixes needed to support some browsers). By default, radio buttons (and checkboxes) are styled with the operating system's native styles for those controls. By specifying appearance: none, you can remove the native styling altogether, and create your own styles for them. Here we've used a {{cssxref("border")}} along with {{cssxref("border-radius")}} and a {{cssxref("transition")}} to create a nice animating radio selection. Notice also how the {{cssxref(":checked")}} pseudo-class is used to specify the styles for the radio button's appearance when selected.
Compatibility note: If you wish to use the {{cssxref("appearance")}} property, you should test it very carefully. Although it is supported in most modern browsers, its implementation varies widely. In older browsers, even the keyword none does not have the same effect across different browsers, and some do not support it at all. The differences are smaller in the newest browsers.
{{EmbedLiveSample('Styling_radio_inputs', 600, 120)}}
Notice that when clicking on a radio button, there's a nice, smooth fade out/in effect as the two buttons change state. In addition, the style and coloring of the legend and submit button are customized to have strong contrast. This might not be a look you'd want in a real web application, but it definitely shows off the possibilities.
| Specification | Status | |
|---|---|---|
| {{SpecName('HTML WHATWG', 'forms.html#radio-button-state-(type=radio)', '<input type="radio">')}} | {{Spec2('HTML WHATWG')}} | |
| {{SpecName('HTML5 W3C', 'forms.html#radio-button-state-(type=radio)', '<input type="radio">')}} | {{Spec2('HTML5 W3C')}} |
{{Compat("html.elements.input.input-radio")}}