using string return values to signal errors #patterns #js

error_pattern.js

// reurn a string message to signal an error  
handleAddOption(option) {
    if (!option) {
      return "Enter valid value";
    } else if (this.state.options.indexOf(option) > -1) {
      return "This option already exists";
    } else {
      this.setState((prevState, props) => {
        return {
          options: [...prevState.options, option]
        };
      });
    }
  }

// elsewhere check the return value; if it's a string
// signal error
const error = handleOption(option);
if (error){ 
  // do something 
}