Lodash is a JavaScript utility library that enhances performance and functionality with arrays, objects, and strings. An underscore prepends the method like this: _.filter.
Express.js is a minimal and flexible Node.js web application framework. It simplifies development and reduces repetitive code.
Promise object is used for asynchronous successes and failures. A promise can have the state of being fulfilled, rejected or pending. A promise takes in one argument, a callback with the two parameters of resolve and reject, and performs something within the callback that invokes the parameters.
Scope is the context of your code dependent upon whether a variable is declared inside or outside a function. Scope can either be global or local.
Lexical Scope is when a function is within another function and the inner function has access to the scope of the outer function. (aka: Static Scope)
Scope chains establish the scope for a given function by determining nested scopes and what scope is associated with what function. The scope chain starts at the innermost scope and works its way outwards.
Closures are created when a function is within another function and the inner function has access to the outer function's variables and parameters. A closure has three scope chains: access to its own scope, access to the outer function's variables, and access to the global variables.