HTMLFormElement - Web APIs 编辑

The HTMLFormElement interface represents a <form> element in the DOM. It allows access to—and, in some cases, modification of—aspects of the form, as well as access to its component elements.

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Properties

This interface also inherits properties from its parent, HTMLElement.

HTMLFormElement.elements Read only

A HTMLFormControlsCollection holding all form controls belonging to this form element.

HTMLFormElement.lengthRead only

A long reflecting the number of controls in the form.

HTMLFormElement.name

A DOMString reflecting the value of the form's name HTML attribute, containing the name of the form.

HTMLFormElement.method

A DOMString reflecting the value of the form's method HTML attribute, indicating the HTTP method used to submit the form. Only specified values can be set.

HTMLFormElement.target

A DOMString reflecting the value of the form's target HTML attribute, indicating where to display the results received from submitting the form.

HTMLFormElement.action

A DOMString reflecting the value of the form's action HTML attribute, containing the URI of a program that processes the information submitted by the form.

HTMLFormElement.encoding or HTMLFormElement.enctype

A DOMString reflecting the value of the form's enctype HTML attribute, indicating the type of content that is used to transmit the form to the server. Only specified values can be set. The two properties are synonyms.

HTMLFormElement.acceptCharset

A DOMString reflecting the value of the form's accept-charset HTML attribute, representing the character encoding that the server accepts.

HTMLFormElement.autocomplete

A DOMString reflecting the value of the form's autocomplete HTML attribute, indicating whether the controls in this form can have their values automatically populated by the browser.

HTMLFormElement.noValidate

A Boolean reflecting the value of the form's novalidate HTML attribute, indicating whether the form should not be validated.

Named inputs are added to their owner form instance as properties, and can overwrite native properties if they share the same name (e.g. a form with an input named action will have its action property return that input instead of the form's action HTML attribute).

Methods

This interface also inherits methods from its parent, HTMLElement.

checkValidity()

Returns true if the element's child controls are subject to constraint validation and satisfy those constraints; returns false if some controls do not satisfy their constraints. Fires an event named invalid at any control that does not satisfy its constraints; such controls are considered invalid if the event is not canceled. It is up to the programmer to decide how to respond to false.

reportValidity()

Returns true if the element's child controls satisfy their validation constraints. When false is returned, cancelable invalid events are fired for each invalid child and validation problems are reported to the user.

requestSubmit()

Requests that the form be submitted using the specified submit button and its corresponding configuration.

reset()

Resets the form to its initial state.

submit()

Submits the form to the server.

Deprecated methods

HTMLFormElement.requestAutocomplete()

Triggers a native browser interface to assist the user in completing the fields which have an autofill field name value that is not off or on. The form will receive an event once the user has finished with the interface, the event will either be autocomplete when the fields have been filled or autocompleteerror when there was a problem.

Events

Listen to these events using addEventListener(), or by assigning an event listener to the oneventname property of this interface.

formdata

The formdata event fires after the entry list representing the form's data is constructed.
Also available via the onformdata property.

reset

The reset event fires when a form is reset.
Also available via the onreset property.

submit

The submit event fires when a form is submitted.
Also available via the onsubmit property.

Usage notes

Obtaining a form element object

To obtain an HTMLFormElement object, you can use a CSS selector with querySelector(), or you can get a list of all of the forms in the document using its forms property.

Document.forms returns an array of HTMLFormElement objects listing each of the forms on the page. You can then use any of the following syntaxes to get an individual form:

document.forms[index]

Returns the form at the specified index into the array of forms.

document.forms[id]

Returns the form whose ID is id.

document.forms[name]

Returns the form whose name attribute's value is name.

Accessing the form's elements

You can access the list of the form's data-containing elements by examining the form's elements property. This returns an HTMLFormControlsCollection listing all of the form's user data entry elements, both those which are descendants of the <form> and those which are made members of the form using their form attributes.

You can also get the form's element by using its name attribute as a key of the form, but using elements is a better approach—it contains only the form's elements, and it cannot be mixed with other attributes of the form.

Issues with Naming Elements

Some names will interfere with JavaScript access to the form’s properties and elements.

For example:

• <input name="id"> will take precedence over <form id="…">. This means that form.id will not refer to the form’s id, but to the element whose name is "id". This will be the case with any other form properties, such as <input name="action"> or <input name="post">.
• <input name="elements"> will render the form’s elements collection inaccessible. The reference form.elements will now refer to the individual element.

To avoid such problems with element names:

• Always use the elements collection to avoid ambiguity between an element name and a form property.
• Never use "elements" as an element name.

If you are not using JavaScript, this will not cause a problem.

Elements that are considered form controls

The elements included by HTMLFormElement.elements and HTMLFormElement.length are the following:

• <button>
• <fieldset>
• <input> (with the exception that any whose type is "image" are omitted for historical reasons)
• <object>
• <output>
• <select>
• <textarea>

No other elements are included in the list returned by elements, which makes it an excellent way to get at the elements most important when processing forms.

Examples

Creating a new form element, modifying its attributes, then submitting it:

const f = document.createElement("form"); // Create a form
document.body.appendChild(f);             // Add it to the document body
f.action = "/cgi-bin/some.cgi";           // Add action and method attributes
f.method = "POST";
f.submit();                               // Call the form's submit() method

Extract information from a <form> element and set some of its attributes:

<form name="formA" action="/cgi-bin/test" method="post">
 <p>Press "Info" for form details, or "Set" to change those details.</p>
 <p>
  <button type="button" onclick="getFormInfo();">Info</button>
  <button type="button" onclick="setFormInfo(this.form);">Set</button>
  <button type="reset">Reset</button>
 </p>

 <textarea id="form-info" rows="15" cols="20"></textarea>
</form>

<script>
  function getFormInfo(){
    // Get a reference to the form via its name
    var f = document.forms["formA"];
    // The form properties we're interested in
    var properties = [ 'elements', 'length', 'name', 'charset', 'action', 'acceptCharset', 'action', 'enctype', 'method', 'target' ];
    // Iterate over the properties, turning them into a string that we can display to the user
    var info = properties.map(function(property) { return property + ": " + f[property] }).join("\n");

    // Set the form's <textarea> to display the form's properties
    document.forms["formA"].elements['form-info'].value = info; // document.forms["formA"]['form-info'].value would also work
  }

  function setFormInfo(f){ // Argument should be a form element reference.
    f.action = "a-different-url.cgi";
    f.name   = "a-different-name";
  }
</script>

Submit a <form> into a new window:

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Example new-window form submission</title>
</head>
<body>

<form action="test.php" target="_blank">
  <p><label>First name: <input type="text" name="firstname"></label></p>
  <p><label>Last name: <input type="text" name="lastname"></label></p>
  <p><label><input type="password" name="pwd"></label></p>

  <fieldset>
   <legend>Pet preference</legend>

    <p><label><input type="radio" name="pet" value="cat"> Cat</label></p>
    <p><label><input type="radio" name="pet" value="dog"> Dog</label></p>
  </fieldset>

  <fieldset>
    <legend>Owned vehicles</legend>

    <p><label><input type="checkbox" name="vehicle" value="Bike">I have a bike</label></p>
    <p><label><input type="checkbox" name="vehicle" value="Car">I have a car</label></p>
  </fieldset>

  <p><button>Submit</button></p>
</form>

</body>
</html>

Submitting forms and uploading files using XMLHttpRequest

If you want to know how to serialize and submit a form using the XMLHttpRequest API, please read this paragraph.

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The HTML element implementing this interface: <form>.