A callback function is a function which is passed to another function as a parameter. This function is then invoked within the calling function, to complete some kind of routine or action. Javascript is a scripting language based on events. Callbacks are a technique of ensuring that a particular code does not run until another code has finished execution.

The main difference is scoping rules. Variables declared with var are scoped to the immediate function body, while let/const variables are scoped to the immediate enclosing block. Var variables are hoisted and initialized to undefined. let variables are not initialized until their definition is evaluated. Accessing them before the initialization results in a ReferenceError. The variable is said to be in “temporal dead zone” from the start of the block until the let is initialized. At the top level, let, unlike var, does not create a property on the global object. let foo = ‘foo’; window.foo; // undefined

Common breakpoints are 320px — 480px for mobile devices, 481px — 768px for iPads & tablets, 769px — 1024px for small screens like laptop, 1025px — 1200px for large screens like Desktops, and 1201px and above for extra large screens like TV. const size = { mobileS: '320px', mobileM: '375px', mobileL: '425px', tablet: '768px', laptop: '1024px', laptopL: '1440px', desktop: '2560px', }; const device = { mobileS: `(min-width: ${size.mobileS})`, mobileM: `(min-width: ${size.mobileM})`, mobileL: `(min-width: ${size.mobileL})`, tablet: `(min-width: ${size.tablet})`, laptop: `(min-width: ${size.laptop})`, laptopL: `(min-width: ${size.laptopL})`, desktop: `(min-width: ${size.desktop})`, desktopL: `(min-width: ${size.desktop})`, };

The Async keyword before a function means that a function returns a promise. The await keyword only works inside Async functions, and makes JS wait until that promise settles and returns its result

Block - Element - Modifiers Block - should represent a block of design, such as a nav, header, footer // should use a hyphen delimiter .stick-man Element - individual elements which make up the block // two underscores .stick-man__head Modifiers - .stick-man--blue // two hyphens

Void functions are functions which do not return a value.

Uniform resource identifier/locator/name URI is the id of a resource

String interpolation is replacing placeholders with values in a string literal, using template literals.