HTML / CSS features allow you to create beautiful and dynamic pages. The JavaScript programming language helps the developer assign functionality to page elements, handle events, organize a dialogue with a visitor, and provide data exchange with the server.
HTML pages and CMS
Modern Internet programming is increasingly using content management systems (Content Management System - CMS). In this case, the connection of any files is solved automatically.
In this example, all buttons added to the site page can be equipped with additional functionality, both through the onclick event, and by connecting an additional script file.
Connection of templates and frameworks (for example, jQuery) is done automatically. JavaScript is an integral part of the browser. Any CMS takes this into account and uses it as efficiently as possible. As a rule, CMS makes full use of the AJAX mechanism, the most advanced JS tools, but leaves the developer with the opportunity to adjust and refine the functionality of the page in the browser, especially to control the processing of events.
Traditional JavaScript to HTML
There are not many options. You can embed the JS code with the script tag in the page itself (3) or connect it as an external file (1). Each option has its own advantages. Typically, developers use both options at the same time.
JavaScript is events, the DOM, and full control over all elements of the page. Option 2 is a direct connection of the JS code to the body of the page, which is triggered when the page is fully loaded.
External files and server management
The formation of an HTML document when developing based on CMS and when manually creating a web resource is programmed. Event processing, creation of page elements and external files can be performed as it is convenient in each case, in real time.
PHP interpreter, forming the page, can create page code, JavaScript-files, pictures, compose the structure of files and folders. Through the scope of variables and data, the developer can switch functionality.
Typically, an HTML document provides several options for working with a visitor. For example, depending on the region, gender, age, etc., you can connect certain features of the site that are convenient and appropriate to have on one page.
In this example, how to connect JavaScript to the HTML elements of the page is shown using mouse events as an example. Such an option of using JS features is sometimes necessary when the functionality of an element needs to be changed during the work of the page.
Page Elements Functionality
JavaScript is focused on servicing events on the elements of the page and the tree of DOM objects (Document Object Model). From this point of view, the question "How to connect JavaScript to HTML elements?" It is decided initially.
For example, all fields of the data entry form can be immediately received by JS-handlers for validating (checking) data for correctness. The date should be a date, a number a number, and a character string should contain only valid characters.
Data entry control is an important feature, and there is no point in solving it in real time and connecting the JS handler while the visitor is on the page. It is advisable to foresee a form in terms of structure, content and functionality of the verification. The task of connecting JavaScript to HTML form elements can be solved immediately.
A different situation will be on the elements when solving the problem of data transfer through the mechanisms of Drag and Drop. In most cases, you have to dynamically change the handlers. Capturing an element to move is one event, actually moving across the boundaries of other elements is another event.
The question of how to connect JavaScript to the HTML elements of the page that “meet along the way” can be not only dynamic, but also unpredictable.
Dynamics and event processing
The peculiarity of JavaScript is initially distributed algorithms and events that can work in the most unpredictable way. A program (script) in JS is by no means a program in C / C ++, PHP or Perl. Conventional programming languages allow events, data type dynamics, parallel computing, but the originality of JS and its close relationship with the DOM brings specificity to programming in this language and, very importantly, the correct placement of the code.
All JS scripts merge into a single space, but the correct placement of variables, functions, event handlers and the sequence of operations is essential.
Using the server-side language PHP inside JavaScript code is more convenient to do when this code is directly inserted into the HTML document. It is not customary to place PHP code inside an external * .js file, although the imagination of a modern developer is not much limited if it works without one or another content management system.
It’s important to keep in mind: JavaScript is initially distributed algorithms and events. Server languages are sequences of operations, algorithms of actions that are executed until the moment the page enters the browser. The answer to the question "How to connect JavaScript to an HTML document?" will depend not only on the logic of the algorithm, but also on the time of the solution.