53 lines
1.5 KiB
Markdown
53 lines
1.5 KiB
Markdown
<!-- Do not edit this file. It is automatically generated by API Documenter. -->
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[Home](./index.md) > [puppeteer](./puppeteer.md) > [Page](./puppeteer.page.md) > [evaluateOnNewDocument](./puppeteer.page.evaluateonnewdocument.md)
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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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<b>Signature:</b>
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```typescript
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evaluateOnNewDocument(pageFunction: Function | string, ...args: unknown[]): Promise<void>;
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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 | Function \| string | Function to be evaluated in browser context |
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| args | unknown\[\] | Arguments to pass to <code>pageFunction</code> |
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<b>Returns:</b>
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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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```js
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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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