Javascript (JS) was invented by the mystical Brendan Eich in only ten days. Grand master Eich created a language that, alongside HTML and CSS, is one of the core technologies of the World Wide Web. JS enables interactive web pages. JS’s strength comes from its functions. For example, a function can receive another function, this is called a ‘callback function’ and keeps code from getting repetitious. JS also allows DOM manipulation. One very useful spell to know is the ‘array.map()’ method, to turn arguments into a manipulable array. Another great spell is ‘array.findIndexOf()’ to help you quickly find an argument in an array.