What is JavaScript?
javascript is the programming language that powers web browsers. Unlike other languages that require compiling, javascript programs can be typed right into HTML and run automatically when the page loads. Its popularity comes from a few key advantages: its simplicity and speed, the fact that errors are easy to spot and fix, and its ability to interact with APIs.
Scripts written in javascript are called “functions”. In the example below, function createParagraph() is invoked when you click one of the buttons. The function will get references to all of the buttons and add click event handlers to them. When a button is clicked, the function will call the click() method of the associated DOM element.
When a script is loaded, the DOM parser and the JavaScript engine will work together to present a live view of the web page to the executing code. They will then update the DOM according to the JavaScript code.
The DOM is a structure that holds the content of a document and all of its related files, images, and other elements. It also contains a set of rules to describe how these elements are displayed on the screen, and how they connect with each other. This makes it possible for a web browser to display a webpage in any desired format.
Initially, javascript was designed to bring life to web pages by making them dynamic. The programs (called scripts) are written right in the page’s HTML and are run immediately without needing any special preparation or compilation. This allows developers to provide a great amount of functionality within a web browser without having to reload the whole page.
As a scripting language, javascript is very powerful and can be used to create everything from simple arcade games to interactive image editors, calculators, project management tools like Asana or Slack, and even real time communication applications such as Google Meet or Zoom. However, it’s important to remember that javascript can also be used by malicious hackers to steal browser cookies, passwords, credit card numbers, or download viruses onto your computer.
There are some very important concepts that you should know before writing javascript, including the scope of variables and functions. Variables can be defined with the var, let, and const keywords or by using the arrow function syntax, which was introduced in ECMAScript 2015. Arrow functions capture their non-local variables by reference, and they cannot be invoked until they are created with a variable that is assigned to them.
It is also important to understand the execution order of a script. Scripts with the async attribute will be executed as soon as they are downloaded, and scripts with the defer attribute will be loaded first, and then executed in the order that they were placed in the