REPL for interactive exploration in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a Node.js REPL session.

Node.js

const repl = require('[1]');
repl.start();

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Apath

Bfs

Chttp

Drepl

Attempts:

3 left

💡 Hint

Common Mistakes

Using other modules like 'fs' or 'http' instead of 'repl'.

Forgetting to require the module before using it.

The Node.js REPL module is named repl. You require it to start an interactive session.

2fill in blank

medium

Complete the code to define a custom command in the Node.js REPL.

Node.js

const repl = require('repl');
const server = repl.start('> ');
server.defineCommand('[1]', {
  help: 'Say hello',
  action() {
    console.log('Hello!');
    this.displayPrompt();
  }
});

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Aclear

Bexit

Chello

Dhelp

Attempts:

3 left

💡 Hint

Common Mistakes

Using built-in commands like 'exit' or 'clear' as custom commands.

Not calling this.displayPrompt() to show the prompt again.

The defineCommand method lets you add a new command. Here, the command is named 'hello'.

3fill in blank

hard

Fix the error in the code to evaluate an expression asynchronously in the REPL.

Node.js

const repl = require('repl');
const server = repl.start('> ');
server.eval = function(cmd, context, filename, callback) {
  Promise.resolve(eval(cmd)).then(result => {
    callback(null, [1]);
  }).catch(err => {
    callback(err);
  });
};

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Aresult

Bcontext

Ccmd

Dfilename

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the original command string instead of the result.

Passing context or filename which are not the evaluation result.

The callback needs the evaluated result to show it in the REPL output.

4fill in blank

hard

Fill both blanks to create a REPL with a custom prompt and exit message.

Node.js

const repl = require('repl');
const server = repl.start({ prompt: '[1]', useColors: true });
server.on('[2]', () => {
  console.log('Goodbye!');
  process.exit();
});

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A>

Bexit

Cline

Dclose

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'exit' event which does not exist on REPL server.

Setting prompt to something other than '> '.

The prompt sets the REPL prompt string. The close event triggers when the REPL exits.

5fill in blank

hard

Fill all three blanks to create a REPL that saves context variables and uses a custom eval function.

Node.js

const repl = require('repl');
const context = { count: 0 };
function customEval(cmd, context, filename, callback) {
  try {
    const result = eval(cmd);
    callback(null, result);
  } catch (e) {
    callback(e);
  }
}
const server = repl.start({ prompt: '[1]', eval: [2] });
Object.assign(server.context, [3]);

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A>>>

BcustomEval

Ccontext

DreplEval

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong prompt string or missing spaces.

Passing wrong function name for eval.

Not assigning the context object to the REPL context.

The prompt is set to '>>> '. The custom eval function is named customEval. The context object is assigned to the REPL context.