Also, since setState automatically merges a partial state into the current state , we only needed to call it with the changed parts. Specifying the value prop on a controlled component prevents the user from changing the input unless you desire so. The following code demonstrates this. The input is locked at first but becomes editable after a short delay. It can sometimes be tedious to use controlled components, because you need to write an event handler for every way your data can change and pipe all of the input state through a React component.
This can become particularly annoying when you are converting a preexisting codebase to React, or integrating a React application with a non-React library.
In these situations, you might want to check out uncontrolled components , an alternative technique for implementing input forms. Is this page useful? Also note that the default width of an input field is 20 characters. Notice that each input field must have a name attribute to be submitted.
If the name attribute is omitted, the value of the input field will not be sent at all. We just launched W3Schools videos. Get certified by completing a course today! Net, Ruby, etc. Just pick the one you like best. That said, it's worth noting that it's very uncommon to use these technologies directly because this can be tricky. It's more common to use one of the many high quality frameworks that make handling forms easier, such as:.
It's worth noting that even using these frameworks, working with forms isn't necessarily easy. But it's much easier than trying to write all the functionality yourself from scratch, and will save you a lot of time. Note: It is beyond the scope of this article to teach you any server-side languages or frameworks.
The links above will give you some help, should you wish to learn them. Sending files with HTML forms is a special case.
Files are binary data — or considered as such — whereas all other data is text data. Because HTTP is a text protocol, there are special requirements for handling binary data. This attribute lets you specify the value of the Content-Type HTTP header included in the request generated when the form is submitted.
This header is very important because it tells the server what kind of data is being sent. In human terms, this means: "This is form data that has been encoded into URL parameters.
Note: Servers can be configured with a size limit for files and HTTP requests in order to prevent abuse. Each time you send data to a server, you need to consider security. HTML forms are by far the most common server attack vectors places where attacks can occur.
The problems never come from the HTML forms themselves — they come from how the server handles data. The Website security article of our server-side learning topic discusses a number of common attacks and potential defenses against them in detail.
You should go and check that article out, to get an idea of what's possible. So, how do you fight these threats? This is a topic far beyond this guide, but there are a few rules to keep in mind. The most important rule is: never ever trust your users, including yourself; even a trusted user could have been hijacked. Don't assume that you've seen all the possible problems.
As we'd alluded to above, sending form data is easy, but securing an application can be tricky. Just remember that a front-end developer is not the one who should define the security model of the data. The control's "current value" is first set to the initial value.
Thereafter, the control's current value may be modified through user interaction and scripts. A control's initial value does not change. Thus, when a form is reset, each control's current value is reset to its initial value. If a control does not have an initial value, the effect of a form reset on that control is undefined. When a form is submitted for processing, some controls have their name paired with their current value and these pairs are submitted with the form.
Authors should specify the scripting language of a push button script through a default script declaration with the META element. Please consult the definitions of these elements for details about specifying different button types.
Several checkboxes in a form may share the same control name. Thus, for example, checkboxes allow users to select several values for the same property. Since user agent behavior differs, authors should ensure that in each set of radio buttons that one is initially "on". The elements used to create controls generally appear inside a FORM element, but may also appear outside of a FORM element declaration when they are used to build user interfaces.
This is discussed in the section on intrinsic events. Note that controls outside a form cannot be successful controls. User agents may interpret this value as the character encoding that was used to transmit the document containing this FORM element. The FORM element acts as a container for controls. It specifies:. A form can contain text and markup paragraphs, lists, etc. The following example shows a form that is to be processed by the "adduser" program when submitted.
The form will be sent to the program using the HTTP "post" method. Please consult the section on form submission for information about how user agents must prepare form data for servers and how user agents should handle expected responses. Further discussion on the behavior of servers that receive form data is beyond the scope of this specification.
Application designers should note that this mechanism affords only light security protection. Although the password is masked by user agents from casual observers, it is transmitted to the server in clear text, and may be read by anyone with low-level access to the network. When a pointing device is used to click on the image, the form is submitted and the click coordinates passed to the server. The x value is measured in pixels from the left of the image, and the y value in pixels from the top of the image.
The submitted data includes name. If the server takes different actions depending on the location clicked, users of non-graphical browsers will be disadvantaged.
For this reason, authors should consider alternate approaches:. The following sample HTML fragment defines a simple form that allows the user to enter a first name, last name, email address, and gender. When the submit button is activated, the form will be sent to the program specified by the action attribute. In this next example, the JavaScript function name verify is triggered when the "onclick" event occurs:. Please consult the section on intrinsic events for more information about scripting and events.
The following example shows how the contents of a user-specified file may be submitted with a form. The user is prompted for his or her name and a list of file names whose contents should be submitted with the form. The buttons contain images by way of the IMG element. Recall that authors must provide alternate text for an IMG element.
This is particularly helpful when the user must choose from a long list of options; groups of related choices are easier to grasp and remember than a single long list of options.
Zero or more choices may be pre-selected for the user. User agents should determine which choices are pre-selected as follows:. Implementors are advised that future versions of HTML may extend the grouping mechanism to allow for nested groups i. This will allow authors to represent a richer hierarchy of choices. When rendering a menu choice , user agents should use the value of the label attribute of the OPTION element as the choice.
In this example, we create a menu that allows the user to select which of seven software components to install. The first and second components are pre-selected but may be deselected by the user. The remaining components are not pre-selected.
The size attribute states that the menu should only have 4 rows even though the user may select from among 7 options. The other options should be made available through a scrolling mechanism. Only selected options will be successful using the control name "component-select".
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