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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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34
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 provided. This can be used, for instance, to implement fully customized REPL
applications. 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 ```mjs
import repl from 'node:repl'; import repl from 'node:repl';
@ -312,8 +324,12 @@ function byThePowerOfTwo(number) {
return number * number; return number * number;
} }
function myEval(cmd, context, filename, callback) { function myEval(code, context, replResourceName, callback) {
callback(null, byThePowerOfTwo(cmd)); if (Number.isNaN(code)) {
callback(new Error(`${code.trim()} is not a number`));
} else {
callback(null, byThePowerOfTwo(code));
}
} }
repl.start({ prompt: 'Enter a number: ', eval: myEval }); repl.start({ prompt: 'Enter a number: ', eval: myEval });
@ -326,8 +342,12 @@ function byThePowerOfTwo(number) {
return number * number; return number * number;
} }
function myEval(cmd, context, filename, callback) { function myEval(code, context, replResourceName, callback) {
callback(null, byThePowerOfTwo(cmd)); if (Number.isNaN(code)) {
callback(new Error(`${code.trim()} is not a number`));
} else {
callback(null, byThePowerOfTwo(code));
}
} }
repl.start({ prompt: 'Enter a number: ', eval: myEval }); 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 * `eval` {Function} The function to be used when evaluating each given line
of input. **Default:** an async wrapper for the JavaScript `eval()` of input. **Default:** an async wrapper for the JavaScript `eval()`
function. An `eval` function can error with `repl.Recoverable` to indicate 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` * `useColors` {boolean} If `true`, specifies that the default `writer`
function should include ANSI color styling to REPL output. If a custom function should include ANSI color styling to REPL output. If a custom
`writer` function is provided then this has no effect. **Default:** checking `writer` function is provided then this has no effect. **Default:** checking
@ -914,4 +935,5 @@ avoiding open network interfaces.
[`repl.start()`]: #replstartoptions [`repl.start()`]: #replstartoptions
[`reverse-i-search`]: #reverse-i-search [`reverse-i-search`]: #reverse-i-search
[`util.inspect()`]: util.md#utilinspectobject-options [`util.inspect()`]: util.md#utilinspectobject-options
[custom evaluation functions]: #custom-evaluation-functions
[stream]: stream.md [stream]: stream.md