Формы на веб-страницах: устройство и обработка данных

Input fields on a Web page
A webform, web form or HTML form on a web page allows a user to enter data that is sent to a server for processing. Forms can resemble paper or database forms because web users fill out the forms using checkboxes, radio buttons, or text fields. For example, forms can be used to enter shipping or credit card data to order a product, or can be used to retrieve search results from a search engine.

Forms are enclosed in the HTML <form> element. This HTML element specifies the communication endpoint the data entered into the form should be submitted to, and the method of submitting the data, GET or POST.

When data that has been entered into HTML forms is submitted, the names and values in the form elements are encoded and sent to the server in an HTTP request message using GET or POST. Historically, an email transport was also used. The default MIME type (internet media type), application/x www form urlencoded, is based on a very early version of the general URI percent encoding rules, with a number of modifications such as newline normalization and replacing spaces with "+" instead of "%20". Another possible encoding, Internet media type multipart/form data, is also available and is common for POST based file submissions.

Forms are usually combined with programs written in various programming language to allow developers to create dynamic web sites. The most popular languages include both client side and/or server side languages. Although any programming language can be used on the server to process a form's data, the most commonly used languages are scripting languages, which tend to have stronger string handling functionality than programming languages such as C, and also have automatic memory management which helps to prevent buffer overrun attacks.

The de facto client side scripting language for web sites is JavaScript. Using JavaScript on the Document Object Model (DOM) leads to the method of Dynamic HTML that allows dynamic creation and modification of a web page within the browser. While client side languages used in conjunction with forms are limited, they often can serve to do pre validation of the form data and/or to prepare the form data to send to a server side program. This usage is being replaced, however, by HTML5's new input field types and required attribute.

Server side code can do a vast assortment of tasks to create dynamic web sites that, for technical or security reasons, client side code cannot — from authenticating a login, to retrieving and storing data in a database, to spell checking, to sending e mail. A significant advantage to server side over client side execution is the concentration of functionality onto the server rather than relying on different web browsers to implement various functions in consistent, standardized ways. In addition, processing forms on a server often results in increased security if server side execution is designed not to trust the data supplied by the client and includes such techniques as HTML sanitization. One disadvantage to server side code is scalability—server side processing for all users occurs on the server, while client side processing occurs on individual client computers.

Some of the interpreted languages commonly used to design interactive forms in web development are PHP, Python, Ruby, Perl, JSP, Adobe ColdFusion and some of the compiled languages commonly used are Java and C# with ASP. NET.

Among the simplest and most commonly needed types of server side script is that which simply emails the contents of a submitted form. This kind of script is frequently exploited by spammers, however, and many of the most popular form to email scripts in use are vulnerable to hijacking for the purpose of sending spam emails. One of the most popular scripts of this type was "FormMail. pl" made by Matt's Script Archive. Today, this script is no longer widely used in new development due to lack of updates, security concerns, and difficulty of configuration.

Some companies offer forms as a hosted service. Usually, these companies give some kind of visual editor, reporting tools and infrastructure to create and host the forms, that can be embedded into webpages. Web hosting companies provide templates to their clients as an add on service. Other form hosting services offer free contact forms that a user can install on their own website by pasting the service's code into the site's HTML.

HTML forms were first implemented by the Viola browser.