To be more precise, in JS land, we introduced async not directly because of scripting but because of backwards compatibility - prior to async/Promise, the JS +

To be more precise, in JS land, we introduced async not directly because of scripting but because of backwards compatibility - prior to async/Promise, the JS + DOM semantics were specified with a single thread of execution in mind, with complex dependencies in both directions (e.g. some DOM operations can cause sync reflow while handling an event, which is... bad) and run-to-completion. Promise made it easier to: - cut monolithic chunks of code-that-needs-to-be-executed-to-completion-before-updating-the-screen into something that didn't cause jank; - introduce background I/O. async/await made Promise more readable. (yes, that's for Promise and async/await on the browser, async callbacks have a different history on Node)