skypager-repl/src/extensions/promise.js

an awesome repl

export default (repl, evalFn) => {
  const realEval = evalFn || repl.eval

  const promiseEval = (cmd, context, filename, callback) => {
    realEval.call(repl, cmd, context, filename, (err, res) => {
      // Error response
      if (err) {
        return callback(err)
      }

      if (res && typeof res.value === 'function' && res.constructor.name === 'LodashWrapper') {
        return callback(null, res.value())
      }

      if (!res || typeof res.then != 'function' || (typeof res.then === 'function' && typeof res.context === 'object')) {
        return callback(null, res)
      }

      const cancel = (chunk, key) => {
        repl.outputStream.write('break.\n')
        if (key.name === 'escape') {
          process.stdin.removeListener('keypress', cancel)
          callback(null, res)
          callback = function () {}
        }
      }

      process.stdin.on('keypress', cancel)

      // Start a timer indicating that escape can be used to quit
      const hangTimer = setTimeout(function () {
        repl.outputStream.write('Hit escape to stop waiting on promise\n')
      }, 5000)

      res.then(function (val) {
        process.stdin.removeListener('keypress', cancel)
        clearTimeout(hangTimer)
        callback(null, val)
      }, function (err) {
        process.stdin.removeListener('keypress', cancel)
        clearTimeout(hangTimer)
        repl.outputStream.write('Promise rejected: ')
        callback(err)
      }).then(null, function (uncaught) {
        // Rethrow uncaught exceptions
        process.nextTick(function () {
          throw uncaught
        })
      })
    })
  }

  repl.eval = promiseEval

  repl.commands['promise'] = {
    help: 'Toggle auto-promise unwrapping',
    action () {
      if (repl.eval === promiseEval) {
        this.outputStream.write('Promise auto-eval disabled\n')
        repl.eval = realEval
      } else {
        this.outputStream.write('Promise auto-eval enabled\n')
        repl.eval = promiseEval
      }
      this.displayPrompt()
    },
  }
}