Error and exit handling

Cliffy throws an ValidationError for invalid user input. By default, when a ValidationError is thrown, cliffy prints the auto generated help and the error message and calls Deno.exit(1) to exit the program. This behaviour can be changed by calling .throwErrors() or .noExit().

Throw errors

By default, cliffy prints the help text and calls Deno.exit() when a ValidationError is thrown. You can override this behaviour with the .throwErrors() method. All other errors will be thrown by default.

No exit

The .noExit() method does the same as .throwErrors() but also prevents the command from calling Deno.exit() when the help or version option is called.

Runtime errors

This example will catch only runtime errors.

import { Command } from "https://deno.land/x/cliffy@v0.25.0/command/mod.ts";

const cmd = new Command()
  .option("-p, --pizza-type <type>", "Flavour of pizza.")
  .action(() => {
    throw new Error("Some error happened.");
  });

try {
  cmd.parse();
} catch (error) {
  console.error("[CUSTOM_ERROR]", error);
  Deno.exit(1);
}Copy

$ deno run https://deno.land/x/cliffy@v0.25.0/examples/command/general_error_handling.ts -t
Unknown option "-t". Did you mean option "-h"?
$ deno run https://deno.land/x/cliffy@v0.25.0/examples/command/general_error_handling.ts
[CUSTOM_ERROR] Some error happened.Copy

Validation errors

This example will catch all errors. You can differentiate between runtime and validation errors by checking if the error is an instance of ValidationError. The validation error has a exitCode property that should be used to exit the program.

import {
  Command,
  ValidationError,
} from "https://deno.land/x/cliffy@v0.25.0/command/mod.ts";

const cmd = new Command()
  .throwErrors() // <-- throw also validation errors.
  .option("-p, --pizza-type <type>", "Flavour of pizza.")
  .action(() => {
    throw new Error("Some error happened.");
  });

try {
  cmd.parse();
} catch (error) {
  if (error instanceof ValidationError) {
    cmd.showHelp();
    console.error("Usage error: %s", error.message);
    Deno.exit(error.exitCode);
  } else {
    console.error("Runtime error: %s", error);
    Deno.exit(1);
  }
}Copy

$ deno run https://deno.land/x/cliffy@v0.25.0/examples/command/validation_error_handling.ts -t
Usage error: Unknown option "-t". Did you mean option "-h"?Copy

Custom validation errors

You can throw custom validation errors by throwing an instance of ValidationError. Optional you can define the exit code that should be used when Deno.exit() is called after displaying the auto generated help and the error message.

import {
  Command,
  ValidationError,
} from "https://deno.land/x/cliffy@v0.25.0/command/mod.ts";

const cmd = new Command()
  .option("-c, --color <name:string>", "Choose a color.")
  .action(({ color }) => {
    if (color === "black") {
      throw new ValidationError("Black is not supported.", { exitCode: 1 });
    }
  })
  .parse();Copy

← Build-in commands Generics →

Edit this page on GitHub