react-concurrent-router/esm/SuspendableResource.js

Performant routing embracing React concurrent UI patterns

class SuspendableResource {
  constructor(loader, isModule = false) {
    this.load = () => {
      if (this._result) return this._result;
      if (this._promise) return this._promise;
      this._promise = this._loader().then(result => {
        const returnValue = this._isModule ? result.default || result : result;
        this._result = returnValue;
        return this._result;
      }).catch(error => {
        this._error = error;
      });
      return this._promise;
    };
    this.isLoaded = () => Boolean(this._result);
    this.read = () => {
      if (this._result) return this._result;
      if (this._error) throw this._error;
      if (this._promise) throw this._promise;
      throw this.load();
    };
    this._isModule = isModule;
    this._loader = loader;
    this._promise = null;
    this._result = null;
    this._error = null;
  }
}

export { SuspendableResource as default };