Comment by olliej

> Specifically, a runtime (IMO) is the set of variables and their associated functionality that exist in the global scope, or are expected to be importable in a predictable and standardized way.

All of which is provided by V8 in this example. The global object, math object, "Object" in general, Arrays, etc are all the runtime. All this tutorial series on embedding V8 is doing is instantiating an existing runtime environment and adding using the APIs to insert a few new APIs.

All together you might say you've got a custom runtime as you have the baseline "JS runtime" + some new APIs and that's clearly a new runtime environment that is distinct from the JS environment on a web page, vs. the one in a worker, vs. in node, etc. But that is at best "extending a runtime", not "rolling your own".

Using the embedding APIs provided by a JS runtime as documented and intended, is not "rolling your own". By that definition I could make an app, embed a WebView, and claim I rolled my own browser runtime, which I would hope is more clearly absurd. Or I could "roll my own Command-line" by reading a string from a user, prepending some commands, and then passing it to system().