JavaScript

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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 trademarks of Oracle Corporation, the two languages follow different design principles, and are actively developed by unrelated organizations;

Use[change | change source]

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:

  • Using AJAX in order to load content without refreshing the website;
  • Changing HTML through the Document Object Model
  • Changing CSS
  • Validating inputs of forms and sending them;
  • Tracking users as they move throughout the website;

Frameworks[change | change source]

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;

Beyond web browsers[change | change source]

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;

Syntax[change | change source]

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 const or let are contained within blocks, while variables assigned using var are contained within functions;

// ES5
var x = 1;

// ES6+
const y = 10;
let t = 5;

Examples[change | change source]

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;

Differences between Java and Javascript[change | change source]

  • In Java, to define a variable, you have to say what type of variable it is: a number, a word, a letter, or more; In JavaScript, this is not necessary;
  • In JavaScript, functions are stored as variables (unlike Java); This makes the following code okay in JavaScript:
function sayHi() {
    alert("Hi!");
}

sayBye = function() {
    alert("Bye!");
}

sayHi();
sayBye();
  • JavaScript is interpreted, but Java, in most cases, must be compiled; This means that JavaScript needs to be run by another computer program (an interpreter), but finished Java can be run as its own program;

Related pages[change | change source]

References[change | change source]

  1. ↑ "Stack Overflow Developer Survey 2019". Stack Overflow. Retrieved 2020-03-11.
  2. ↑ "Server-Side Javascript: Back With a Vengeance". ReadWrite. 2009-12-17. Retrieved 2020-03-11.
  3. ↑ "var". MDN Web Docs. Retrieved 2018-03-24.
  4. ↑ "const". MDN Web Docs. Retrieved 2018-03-24.
  5. ↑ "let". MDN Web Docs. Retrieved 2018-03-24.
  6. ↑ [1]

Other websites[change | change source]


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