A JavaScript array is a special type of Object which holds a number-indexed list of values starting with the number 0.

• MDN – Global Objects – Array

CSS preprocessors are technology that combines a scripting language to write CSS with more programming language functionality such as variables, nesting, imports, functions, mixins, and more, with a compiler that will then take the CSS written in the preprocessor language to regular CSS so that it can be interpreted by browsers. Sass is currently the most popular, with Less and Stylus among others as alternatives. Bootstrap 3 was built with Less, and Bootstrap 4 was built with Sass.

• MDN – CSS Preprocessors

Packaging code for production deployment after image compression, mininification, and uglification of the css files to ensure that the components are optimized to conserve space and memory.

An event handler is a routine that is used to deal with the event, allowing a programmer to write code that will be executed when the event occurs.

A function is a block of reuseable code that can be called (or invoked) via the function name from elsewhere in a script.

• W3Schools – Functions

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jQuery is a JavaScript library that is extremely widely used. It provides many different methods for DOM manipulation, event listeners, handling cross-browser issues, and much more. Bootstrap uses jQuery to power its JavaScript plugins.

• jQuery.com

Minification is the process of removing whitespace, line returns, comments, and other parts of a code-containing file (such as JavaScript, HTML, CSS) that is not required by the JavaScript engine to interpret it, so as to make the filesize smaller for transmission over the internet.

Methods that changes the original array. The following are examples of mutating array methods:

push()

unshift()

The Node Package Manager’s package.json file allows you to add scripts to its scripts object that can then automate many repetitive tasks, such as watching SCSS files and compiling them to CSS whenever they are changed.

• NPM Scripts

a method used to remove the last element of an array

Sass is a popular CSS preprocessor that is used to write Bootstrap 4’s own CSS.

• Sass Guide

Uglification is what uglify-js and similar libraries call it when they optimize JavaScript files for speed, a process mainly composed of minification and “mangling” of variables (taking variable names and making them shorter and less human-readable, usually by replacing them with single-letter variables. The opposite of uglification is a process called beautification.

Every once in a while, the word uglification is used as a synonym for minification.

• uglify-js NPM library