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Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com> Co-authored-by: Nikolay Vitkov <nvitkov@chromium.org>
94 lines
1.7 KiB
Markdown
94 lines
1.7 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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abstract evaluateOnNewDocument<
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Params extends unknown[],
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Func extends (...args: Params) => unknown = (...args: Params) => unknown,
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>(
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pageFunction: Func | string,
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...args: Params
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): Promise<NewDocumentScriptEvaluation>;
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}
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```
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## Parameters
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<table><thead><tr><th>
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Parameter
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</th><th>
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Type
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</th><th>
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Description
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</th></tr></thead>
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<tbody><tr><td>
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pageFunction
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</td><td>
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Func \| string
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</td><td>
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Function to be evaluated in browser context
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</td></tr>
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<tr><td>
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args
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</td><td>
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Params
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</td><td>
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Arguments to pass to `pageFunction`
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</td></tr>
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</tbody></table>
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**Returns:**
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Promise<[NewDocumentScriptEvaluation](./puppeteer.newdocumentscriptevaluation.md)>
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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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