8e1c8b9be6
* chore(main): release 17.1.1 * chore: generate versioned docs Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
56 lines
1.6 KiB
Markdown
56 lines
1.6 KiB
Markdown
---
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sidebar_label: Page.evaluateOnNewDocument
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---
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# Page.evaluateOnNewDocument() method
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Adds a function which would be invoked in one of the following scenarios:
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- whenever the page is navigated
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- whenever the child frame is attached or navigated. In this case, the function is invoked in the context of the newly attached frame.
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The function is invoked after the document was created but before any of its scripts were run. This is useful to amend the JavaScript environment, e.g. to seed `Math.random`.
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**Signature:**
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```typescript
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class Page {
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evaluateOnNewDocument<
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Params extends unknown[],
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Func extends (...args: Params) => unknown = (...args: Params) => unknown
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>(pageFunction: Func | string, ...args: Params): Promise<void>;
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}
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```
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## Parameters
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| Parameter | Type | Description |
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| ------------ | -------------- | ---------------------------------------------- |
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| pageFunction | Func \| string | Function to be evaluated in browser context |
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| args | Params | Arguments to pass to <code>pageFunction</code> |
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**Returns:**
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Promise<void>
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## Example
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An example of overriding the navigator.languages property before the page loads:
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```ts
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// preload.js
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// overwrite the `languages` property to use a custom getter
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Object.defineProperty(navigator, 'languages', {
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get: function () {
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return ['en-US', 'en', 'bn'];
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},
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});
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// In your puppeteer script, assuming the preload.js file is
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in same folder of our script
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const preloadFile = fs.readFileSync('./preload.js', 'utf8');
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await page.evaluateOnNewDocument(preloadFile);
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```
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