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doc: document REPL custom eval arguments

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PR-URL: https://github.com/nodejs/node/pull/57690
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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Dario Piotrowicz 2025-04-01 16:18:06 +01:00 committed by Marco Ippolito
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doc/api/repl.md
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@ -303,7 +303,19 @@ When a new [`repl.REPLServer`][] is created, a custom evaluation function may be
provided. This can be used, for instance, to implement fully customized REPL
applications.
The following illustrates an example of a REPL that squares a given number:
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:
```mjs
import repl from 'node:repl';
@ -312,8 +324,12 @@ function byThePowerOfTwo(number) {
return number * number;
}
function myEval(cmd, context, filename, callback) {
callback(null, byThePowerOfTwo(cmd));
function myEval(code, context, replResourceName, callback) {
if (Number.isNaN(code)) {
callback(new Error(`${code.trim()} is not a number`));
} else {
callback(null, byThePowerOfTwo(code));
}
}
repl.start({ prompt: 'Enter a number: ', eval: myEval });
@ -326,8 +342,12 @@ function byThePowerOfTwo(number) {
return number * number;
}
function myEval(cmd, context, filename, callback) {
callback(null, byThePowerOfTwo(cmd));
function myEval(code, context, replResourceName, callback) {
if (Number.isNaN(code)) {
callback(new Error(`${code.trim()} is not a number`));
} else {
callback(null, byThePowerOfTwo(code));
}
}
repl.start({ prompt: 'Enter a number: ', eval: myEval });
@ -691,7 +711,8 @@ changes:
* `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.
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
@ -914,4 +935,5 @@ avoiding open network interfaces.
[`repl.start()`]: #replstartoptions
[`reverse-i-search`]: #reverse-i-search
[`util.inspect()`]: util.md#utilinspectobject-options
[custom evaluation functions]: #custom-evaluation-functions
[stream]: stream.md