provided. This can be used, for instance, to implement fully customized REPL

applications.

An evaluation function accepts the following four arguments:

* `code` {string} The code to be executed (e.g. `1 + 1`).

* `context` {Object} The context in which the code is executed. This can either be the JavaScript `global`

context or a context specific to the REPL instance, depending on the `useGlobal` option.

* `replResourceName` {string} An identifier for the REPL resource associated with the current code

evaluation. This can be useful for debugging purposes.

* `callback` {Function} A function to invoke once the code evaluation is complete. The callback takes two parameters:

* An error object to provide if an error occurred during evaluation, or `null`/`undefined` if no error occurred.

* The result of the code evaluation (this is not relevant if an error is provided).

The following illustrates an example of a REPL that squares a given number, an error is instead printed

if the provided input is not actually a number:

import repl from 'node:repl';

return number * number;

}

function myEval(code, context, replResourceName, callback) {

if (Number.isNaN(code)) {

callback(new Error(`${code.trim()} is not a number`));

} else {

callback(null, byThePowerOfTwo(code));

}

}

repl.start({ prompt: 'Enter a number: ', eval: myEval });

return number * number;

}

function myEval(code, context, replResourceName, callback) {

if (Number.isNaN(code)) {

callback(new Error(`${code.trim()} is not a number`));

} else {

callback(null, byThePowerOfTwo(code));

}

}

repl.start({ prompt: 'Enter a number: ', eval: myEval });

* `eval` {Function} The function to be used when evaluating each given line

of input. **Default:** an async wrapper for the JavaScript `eval()`

function. An `eval` function can error with `repl.Recoverable` to indicate

the input was incomplete and prompt for additional lines. See the

[custom evaluation functions][] section for more details.

* `useColors` {boolean} If `true`, specifies that the default `writer`

function should include ANSI color styling to REPL output. If a custom

`writer` function is provided then this has no effect. **Default:** checking

[`repl.start()`]: #replstartoptions

[`reverse-i-search`]: #reverse-i-search

[`util.inspect()`]: util.md#utilinspectobject-options

[custom evaluation functions]: #custom-evaluation-functions

[stream]: stream.md