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Collection: Common Crawl
JavaScript is a high-level programming language. It was originally designed as a scripting language for websites but became widely adopted as a general-purpose programming language, and is currently the most popular programming language in use[1]. JavaScript is usually found running in a web browser as interactive or automated content, ranging from popup messages and live clocks to large web applications. JavaScript is also commonly used in server-side programming through platforms like Node.js[2], or "embedded" in non-JavaScript applications where the base programming language lacks the high-level functionality that JavaScript offers.
Despite the similarities in name and syntax, JavaScript is not related to the programming language Java. Though the names of both languages are trademarksofOracle Corporation, the two languages follow different design principles, and are actively developed by unrelated organizations.
JavaScript is typically inserted into HTML when used on the web, either directly in the file in a HTML tag, or linking it to a separate file containing the script.
JavaScript, as a full featured scripting language, can be used to provide functionality to a website. Examples include:
A majority of websites use what is known as a framework. Frameworks may allow programming to be easier as more predefined procedures are defined within it. Such a library is jQuery.
JavaScript is also used outside of web browsers. As a scripting language, JavaScript can be used to define the behaviour of applications such as extensions in GNOME Shell.
In addition, there are runtime environments for running JavaScript as a server side programming language. Such an environment is Node.js.
Electron is a framework which allows graphical applications to be made with web technologies, by running on the Chromium browser and Node.js.
A JavaScript program is made of a collection of instructions called "statements". A semicolon marks the end of a statement, and allows multiple statements to be placed on the same line. However, it is typical to write each statement on its own line to keep a program file readable.
Variables can be defined in several ways. In an older version named "ES5", variables are defined using the var keyword.[3] In the newer versions after ES5, variables can be defined using const for constant variables and let for local variables.[4][5] The value of constant variables cannot be re-declared or reassigned. Variables assigned using constorlet are contained within blocks, while variables assigned using var are contained within functions.
1// ES5
2var x = 1;
3
4// ES6+
5const y = 10;
6let t = 5;
The script below prints "Example" on the screen. The lines that start with // are comments, which are used to describe the actions of the program.[6]
function sayHi() {
let name = prompt("What's your name?");
// this name is saved to a variable
alert("Hello " + name);
// whatever the name is, the browser alerts "hello (name)"
// a variable was used (name)
}
sayHi(); // Runs the function sayHi
/* This is also a comment, but it can span multiple lines.
Like this.
*/
In the above code it says "Hello " + name
If you want to put JavaScript in your HTML is, you put between the <script></script> tags. The tags indicate that it is a script and not text to be put onto the web page. The script below inserts the numbers 1 through 10 at the bottom of a webpage:
<!DOCTYPE html>
<head>
<title>Example page</title>
<script> // This is the script tag
for (let counter = 1; counter <= 10; counter++) {
document.body.innerHTML = document.body.innerHTML + counter + "<br>";
/*
This puts the number, then a new line element (<br>),
at the end of the web page.
*/
}
// End javascript: </script>
</head>
<body></body>
The for() loop makes whatever code is between the { and the } happen more than one time. In this case, it keeps looping until numOfTimesAround is equal to 10, then it stops. This means it equals ten. It's a bit confusing at first, but it works.
function sayHi() {
alert("Hi!");
}
sayBye = function() {
alert("Bye!");
}
sayHi();
sayBye();
