Is there a way to transpile TypeScript in memory with Node? I would like to be able to get the generated JavaScript in memory.
Yes. TypeScript provides a a ts.transpileModule function:
const ts = require('typescript');
const source = "let x: string = 'hello world'";
const result = ts.transpileModule(source, { compilerOptions: { module: ts.ModuleKind.CommonJS }});
console.log(result.outputText); // var x = 'hello world';