JS

// RestClient.js

  async getData() {

    const response = await fetch(url);

    if (response.status != 200) {
      throw "Server error (" + response.status + ")";
    }

    const data = await response.json();

    if (data.error) {
      throw data.error;
    }

    return data;
  }

// Outside class
  async myMethod() {
    try {
      const data = await restClient.getData();
    }
    catch (e) {
      console.log('ERROR: ', e)
    }

    console.log('Data recieved:', data);
  }

  otherMethod() {
    myMethod();
    console.log(this.causes.an.error); // This error will be caught by the catch block from myMethod

  }