I can imagine being asked at an interview: What’s the difference between JavaScript engines and JavaScript runtimes? Nicholas C. Zakas says:
A JavaScript engine implements ECMAScript as defined by the ECMA-262 standard. ECMA-262 defines the core functionality of JavaScript without any affordances for input or output. A JavaScript runtime is an ECMAScript host that embeds a JavaScript engine and augments it with additional functionality for input and output, along with anything else the runtime needs. Additional functionality might include the DOM in web browsers or file system access in server-side runtimes.
So a feature like a switch statement is a core part of the standard and implemented by a JavaScript engine. But an API like querySelectorAll is a DOM-specific thing and added on by specific JavaScript runtimes.
