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doc: fix vm.Script createCachedData example

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`Script.createCachedData` and `SourceTextModule.createCachedData`
doesn't serialize JavaScript variables.

PR-URL: https://github.com/nodejs/node/pull/44487
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
This commit is contained in:
Chengzhong Wu 2022-09-12 16:23:53 +08:00 committed by GitHub
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1 changed files with 25 additions and 2 deletions
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doc/api/vm.md
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@ -138,6 +138,16 @@ Creates a code cache that can be used with the `Script` constructor's
`cachedData` option. Returns a `Buffer`. This method may be called at any
time and any number of times.
The code cache of the `Script` doesn't contain any JavaScript observable
states. The code cache is safe to be saved along side the script source and
used to construct new `Script` instances multiple times.
Functions in the `Script` source can be marked as lazily compiled and they are
not compiled at construction of the `Script`. These functions are going to be
compiled when they are invoked the first time. The code cache serializes the
metadata that V8 currently knows about the `Script` that it can use to speed up
future compilations.
```js
const script = new vm.Script(`
function add(a, b) {
@ -147,11 +157,14 @@ function add(a, b) {
const x = add(1, 2);
`);
const cacheWithoutX = script.createCachedData();
const cacheWithoutAdd = script.createCachedData();
// In `cacheWithoutAdd` the function `add()` is marked for full compilation
// upon invocation.
script.runInThisContext();
const cacheWithX = script.createCachedData();
const cacheWithAdd = script.createCachedData();
// `cacheWithAdd` contains fully compiled function `add()`.
```
### `script.runInContext(contextifiedObject[, options])`
@ -792,6 +805,16 @@ Creates a code cache that can be used with the `SourceTextModule` constructor's
`cachedData` option. Returns a `Buffer`. This method may be called any number
of times before the module has been evaluated.
The code cache of the `SourceTextModule` doesn't contain any JavaScript
observable states. The code cache is safe to be saved along side the script
source and used to construct new `SourceTextModule` instances multiple times.
Functions in the `SourceTextModule` source can be marked as lazily compiled
and they are not compiled at construction of the `SourceTextModule`. These
functions are going to be compiled when they are invoked the first time. The
code cache serializes the metadata that V8 currently knows about the
`SourceTextModule` that it can use to speed up future compilations.
```js
// Create an initial module
const module = new vm.SourceTextModule('const a = 1;');