feat(fetch-jsonp): bring up

src/fetch-jsonp/index.ts

@@ -0,0 +1,62 @@
+declare global {
+  interface Window {
+    __foxact_jsonp_callbacks__SECRET_INTERNAL_DO_NOT_USE_OR_YOU_WILL_BE_FIRED: Record<string, ((data: any) => void) | undefined>
+  }
+}
+
+const INTERNAL = '__foxact_jsonp_callbacks__SECRET_INTERNAL_DO_NOT_USE_OR_YOU_WILL_BE_FIRED';
+
+export function fetchJsonp<T>(getUrl: (callbackName: string) => string) {
+  if (typeof window === 'undefined') {
+    throw new TypeError('fetchJsonp is only available in the browser');
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition -- initialization
+  if (!window[INTERNAL]) {
+    Object.defineProperty(window, INTERNAL, {
+      value: {},
+      writable: true,
+      configurable: true,
+      enumerable: false
+    });
+  }
+
+  const callbackName = `$${Date.now()}_${Math.random().toString().slice(2)}$`;
+  const fullCallbackName = `window.${INTERNAL}.${callbackName}`;
+  // eslint-disable-next-line prefer-object-has-own -- conflict check
+  if (Object.prototype.hasOwnProperty.call(window[INTERNAL], callbackName)) {
+    throw new TypeError(`Callback name conflict: ${callbackName}`);
+  }
+
+  const url = getUrl(fullCallbackName);
+
+  return new Promise<T>((resolve, reject) => {
+    const script = document.createElement('script');
+    script.src = url;
+    script.async = true;
+
+    const cleanup = () => {
+      script.removeEventListener('error', handleScriptError);
+      script.remove();
+
+      if (window[INTERNAL][callbackName]) {
+        // eslint-disable-next-line @typescript-eslint/no-dynamic-delete -- cleanup
+        delete window[INTERNAL][callbackName];
+      }
+    };
+
+    function handleScriptError() {
+      cleanup();
+      reject(new Error(`Failed to load script: ${url}`));
+    };
+
+    script.addEventListener('error', handleScriptError);
+
+    window[INTERNAL][callbackName] = (data: T) => {
+      cleanup();
+      resolve(data);
+    };
+
+    document.body.append(script);
+  });
+}