Comment by olliej

You're right an interpreter is not a runtime. However V8, JSC, SM, ... aren't just providing you an execution engine. E.g. they are providing all the core objects, APIs, etc that are equivalently provided by the "Visual Studio Redistributables for C++" which you seem happy to call a runtime.

The lack of direct IO is irrelevant. You can take any of these libraries, and execute arbitrary JS, and then display the output (Serenity's spreadsheet uses LibJS for equation cells IIRC). E.g. JS that runs and uses the "runtime environment" to do things.

Your particular use case may benefit from exposing some additional APIs to JS, and all these libraries allow you to do that. But exposing, for example, printf to a full JS runtime environment does not mean you've made a runtime. The belief that for something to be a "runtime" it must have built in IO routines me that no generally usable scripting environment could be a runtime.