repl-preview

Preview output results in a REPL context.

Installation

$ npm install repl-preview

Usage

const { preview } = require('repl-preview')
const keypress = require('repl-preview/keypress') // optional
const repl = require('repl')

const server = repl.start()
keypress(server, (line, key) => {
  // run generic JavaScript in VM
  // or preview custom programming language here
  try {
    const result = vm.runInContext(vm.createContent({ ...server.context }), line)
    preview(server, result)
  } catch (err) {
    // handle possible error
  }
})

API

preview(server, result[, opts])

Renders a preview of a mixed result value with the output truncated to fit the viewport of the terminal.

const { preview } = require('repl-preview')
const { inspect } = require('util')

preview(server, result, {
  // truncates output by default
  truncate: true,

  // default result value pretty handler
  pretty(value) {
    return inspect(value, {
      getters: true,
      colors: true,
      sorted: true,
      depth: 3,
      ...opts
    })
  },

  // default result error handler, called upon render failure
  onerror(err) {
    throw err
  }
})

keypress(stdin, onkeypress)

Creates a 'keypress' listener on for a given stdin stream.

const keypress = require('repl-preview/keypress')

// preview eval'd input from context swalling errors
keypress(server.input, (line, key) => {
  try {
    const context = vm.createContent({ ...server.context })
    const result = vm.runInContext(context, line)
    preview(server, result)
  } catch (err) {
    // handle possible error
  }
})

Example

In the included example, a fake filesystem is contrived and JSONata is used as a query syntax to query the filesystem paths. The query syntax is preprocessed to allow / in place of . so file path queries feel like normal path traversal like:

> /var/log
[
  '/var/log/reboot_ai.mxu',
  '/var/log/research_forward.rcprofile',
  '/var/log/circuit.ipfix',
  '/var/log/security_maroon.mime',
  '/var/log/matrix_infrastructure_payment.mbk'
]

License

MIT