readline.createInterface()

readline.createInterface(options)

Creates a readline Interface instance. Accepts an options Object that takes the following values:

• input - the readable stream to listen to (Required).

• output - the writable stream to write readline data to (Optional).

• completer - an optional function that is used for Tab autocompletion. See below for an example of using this.

• terminal - pass true if the input and output streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Defaults to checking isTTY on the output stream upon instantiation.

• historySize - maximum number of history lines retained. Defaults to 30.

The completer function is given the current line entered by the user, and is supposed to return an Array with 2 entries:

1. An Array with matching entries for the completion.

2. The substring that was used for the matching.

Which ends up looking something like: [[substr1, substr2, ...], originalsubstring].

Example:

function completer(line) {
  var completions = '.help .error .exit .quit .q'.split(' ')
  var hits = completions.filter((c) => { return c.indexOf(line) == 0 })
  // show all completions if none found
  return [hits.length ? hits : completions, line]
}

Also completer can be run in async mode if it accepts two arguments:

function completer(linePartial, callback) {
  callback(null, [['123'], linePartial]);
}

createInterface is commonly used with process.stdin and process.stdout in order to accept user input:

const readline = require('readline');
const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

Once you have a readline instance, you most commonly listen for the 'line' event.

If terminal is true for this instance then the output stream will get the best compatibility if it defines an output.columns property, and fires a 'resize' event on the output if/when the columns ever change (process.stdout does this automatically when it is a TTY).