https://rcoedo.com/blog/2018/08/06/mastering-the-node-js-repl-part-two

Examples for "Mastering the Node.js REPL, Part Two"

This gist contains the examples for the article "Mastering the Node.js REPL, Part Two".

- https://medium.com/trabe/mastering-the-node-js-repl-part-2-365c52a5203d
- https://rcoedo.com/blog/2018/08/06/mastering-the-node-js-repl-part-two

repl-1.js

const Repl = require("repl");

// Print the welcome message
console.log(`
  Hello, ${process.env.USER}!
  You're running the Node.js REPL in ${process.cwd()}.
`);

// Start the REPL
Repl.start();

repl-2.js

const Repl = require("repl");

// Color functions
const colors = { RED: "31", GREEN: "32", YELLOW: "33", BLUE: "34", MAGENTA: "35" };
const colorize = (color, s) => `\x1b[${color}m${s}\x1b[0m`;

// Some useful stuff
const user = colorize(colors.MAGENTA, process.env.USER);
const cwd = colorize(colors.YELLOW, process.cwd());
const say = message => () => console.log(message);
const sayWelcome = say(`
  Hello, ${user}!
  You're running the Node.js REPL in ${cwd}.
`);

// Print the welcome message
sayWelcome();

// Start the REPL
Repl.start();

repl-3.js

const nodeVersion = colorize(colors.GREEN, `${process.title} ${process.version}`);
const prompt = `${nodeVersion} → `;

// Start the REPL
Repl.start({ prompt });

repl-4.js

// Our goodbye function
const sayBye = say(`
  Goodbye, ${user}!
`);

// Start the REPL
const repl = Repl.start({ prompt });

// Listen for the exit event
repl.on("exit", sayBye);

repl-5.js

const util = require("util");

// Start the REPL
const repl = Repl.start({ prompt });

repl.context.noop = () => {};
repl.context.identity = x => x;
repl.context.isString = x => typeof x === "string" || x instanceof String;
repl.context.timeout = util.promisify(setTimeout);

repl-6.js

// Function that takes an object o1 and returns another function
// that takes an object o2 to extend it with the o1 properties as
// read-only
const extendWith = properties => context => {
  Object.entries(properties).forEach(([k, v]) => {
    Object.defineProperty(context, k, {
      configurable: false,
      enumerable: true,
      value: v,
    });
  });
};

// Start the REPL
const repl = Repl.start({ prompt });

// Extend the REPL context as read-only
extendWith({
  noop: () => {},
  identity: x => x,
  isString: x => typeof x === "string" || x instanceof String,
  timeout: util.promisify(setTimeout),
})(repl.context);

repl-7.js

// Context initializer
const initializeContext = extendWith({
  utils: {
    noop: () => {},
    identity: x => x,
    isString: x => typeof x === "string" || x instanceof String,
    timeout: util.promisify(setTimeout),
  },
});

// Start the REPL
const repl = Repl.start({ prompt });

// Initialize our context
initializeContext(repl.context);

// Listen for the reset event
repl.on("reset", initializeContext);

repl-8.js

// Start the REPL
const repl = Repl.start({ prompt });

// Define our custom commands
repl.defineCommand("welcome", {
  help: "Prints the welcome message again",
  action() {
    this.clearBufferedCommand();
    sayWelcome();
    this.displayPrompt();
  },
});

repl-define-property.js

// Start the REPL
const repl = Repl.start({ prompt });

Object.defineProperty(repl.context, "noop", {
  configurable: false,
  enumerable: true,
  value: () => {},
});

repl-final.js

const Repl = require("repl");
const util = require("util");

// Color functions
const colors = { RED: "31", GREEN: "32", YELLOW: "33", BLUE: "34", MAGENTA: "35" };
const colorize = (color, s) => `\x1b[${color}m${s}\x1b[0m`;

// Function that takes an object o1 and returns another function
// that takes an object o2 to extend it with the o1 properties as
// read-only
const extendWith = properties => context => {
  Object.entries(properties).forEach(([k, v]) => {
    Object.defineProperty(context, k, {
      configurable: false,
      enumerable: true,
      value: v,
    });
  });
};

// Function that takes an object o1 with shape { key: command } and
// returns another function that takes the repl and defines the commands
// in it
const defineCommands = commands => repl => {
  Object.entries(commands).forEach(([k, v]) => {
    repl.defineCommand(k, v);
  });
};

// Context initializer
const initializeContext = extendWith({
  noop: () => {},
  identity: x => x,
  isString: x => typeof x === "string" || x instanceof String,
  timeout: util.promisify(setTimeout),
});

// Some useful stuff
const user = colorize(colors.MAGENTA, process.env.USER);
const cwd = colorize(colors.YELLOW, process.cwd());
const say = message => () => console.log(message);
const sayWelcome = say(`
  Hello, ${user}!
  You're running the Node.js REPL in ${cwd}.
`);
const sayBye = say(`
  Goodbye, ${user}!
`);
const nodeVersion = colorize(colors.GREEN, `${process.title} ${process.version}`);
const prompt = `${nodeVersion} → `;

// Print the welcome message
sayWelcome();

// Start the REPL
const repl = Repl.start({ prompt });

// Initialize our context
initializeContext(repl.context);

// Define our custom commands
defineCommands({
  welcome: {
    help: "Prints the welcome message",
    action() {
      this.clearBufferedCommand();
      sayWelcome();
      this.displayPrompt();
    },
  },
})(repl);

// Listen for the server events
repl.on("reset", initializeContext);
repl.on("exit", sayBye);

repl-global-context.js

const Repl = require("repl");

global.noop = () => {};
global.identity = x => x;
global.isString = x => typeof x === "string" || x instanceof String;

const repl = Repl.start({ useGlobal: true });