グローバル、fetchの利用可否、ファイル・ネットワークAPI

全体像

安全な実行環境の判定

// Detect presence of common globals
const hasWindow = typeof window !== "undefined";
const hasGlobal = typeof global !== "undefined";
const hasProcess = typeof process !== "undefined" && process && typeof process.version === "string";

console.log("globalThis exists?", typeof globalThis !== "undefined");
console.log("window?", hasWindow);
console.log("global?", hasGlobal);
console.log("Node process?", hasProcess);

fetch: 機能検出

// Feature-detect fetch; do not assume it exists everywhere
const hasFetch = typeof fetch === "function";
console.log("fetch available?", hasFetch);

// If available, you could call fetch(...). For a safe demo we only log.
if (!hasFetch) {
  console.log("Provide a fallback or use a library in Node versions without fetch.");
}

ファイル: Nodeとブラウザー

// Files are a Node concern; browsers cannot read your disk directly
const hasRequire = typeof require === "function";
console.log("CommonJS require available?", hasRequire);

// Safe message instead of real file I/O (keeps the demo runnable everywhere)
if (hasRequire) {
  console.log("In Node you can use fs for files; in browsers you cannot.");
} else {
  console.log("No require here; likely a browser-like or sandboxed runtime.");
}

共通: URL API

// URL is available in both environments
const u = new URL("https://example.com/path?x=1#top");
console.log("host:", u.host);
console.log("pathname:", u.pathname);
console.log("search:", u.search);
console.log("hash:", u.hash);

初心者向けの習慣

fetch検出クイズ

まとめ