TypeScript type guards

error-types.ts

class NetworkError extends Error {}

class OtherError extends Error {}

function flipCoin() {
  return Math.random() > 0.7;
}

function networkRequest() {
  if (flipCoin()) {
    throw new NetworkError('Network error ...');
  }
  return 'Network OK';
}

function otherFunction() {
  if (flipCoin()) {
    throw new OtherError('Other error ...');
  }
  return 'Other OK';
}

try {
  const networkResult = networkRequest();
  console.log('network result ->', networkResult);
  const otherResult = otherFunction();
  console.log('other result ->', otherResult);
  throw new Error('this is another error');
} catch(err) {
  if (err instanceof NetworkError) {
    console.log('Error is a NetworkError -> ', err);
  } else if (err instanceof OtherError) {
    console.log('Error is a OtherError -> ', err);
  } else {
    console.log('Error is something else ->', err)
  }
}

pad-left.ts

// padLeft(3, 'x') => '   x'
// padLeft('.', 'x') => '.x'

function padLeft(padding: number | string, input: string): string {
  if (typeof padding === 'number') {
    return new Array(padding + 1).join(" ") + input;
  }
  return padding + input;
}

console.log(padLeft(10, 'x'));
console.log(padLeft('...', 'y'));
// console.log(padLeft({}, 'x'));

// console.log('test' + 5)

// console.log(new Array(5));
// console.log(new Array('toto'));