What is JavaScript? Engines (V8/SpiderMonkey) & Runtimes (Browser vs Node)

// First tiny program: prints a greeting
function greet(name) {
  return "Hello, " + name + "!";
}

const msg = greet("CoddyKit");
console.log(msg);

// Detect where code runs using simple globals
const inBrowser = typeof window !== "undefined" && typeof document !== "undefined";
const inNode = typeof process !== "undefined" && typeof process.versions === "object";

if (inBrowser) {
  console.log("Runtime: Browser (DOM available).");
}
if (inNode) {
  console.log("Runtime: Node (filesystem APIs available).");
}

// Use the right output method for each runtime
const text = "JS runs in different environments!";
const canAlert = typeof alert === "function";

if (canAlert) {
  alert(text); // Browser popup
} else {
  console.log(text); // Works in Node and browsers
}