80 lines
3.0 KiB
Markdown
80 lines
3.0 KiB
Markdown
---
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sidebar_label: Page.$eval
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---
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# Page.$eval() method
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This method runs `document.querySelector` within the page and passes the result as the first argument to the `pageFunction`.
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**Signature:**
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```typescript
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class Page {
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$eval<
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Selector extends string,
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Params extends unknown[],
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Func extends EvaluateFunc<
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[ElementHandle<NodeFor<Selector>>, ...Params]
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> = EvaluateFunc<[ElementHandle<NodeFor<Selector>>, ...Params]>
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>(
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selector: Selector,
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pageFunction: Func | string,
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...args: Params
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): Promise<Awaited<ReturnType<Func>>>;
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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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| selector | Selector | the [selector](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Selectors) to query for |
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| pageFunction | Func \| string | the function to be evaluated in the page context. Will be passed the result of <code>document.querySelector(selector)</code> as its first argument. |
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| args | Params | any additional arguments to pass through to <code>pageFunction</code>. |
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**Returns:**
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Promise<Awaited<ReturnType<Func>>>
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The result of calling `pageFunction`. If it returns an element it is wrapped in an [ElementHandle](./puppeteer.elementhandle.md), else the raw value itself is returned.
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## Remarks
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If no element is found matching `selector`, the method will throw an error.
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If `pageFunction` returns a promise `$eval` will wait for the promise to resolve and then return its value.
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## Example 1
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```ts
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const searchValue = await page.$eval('#search', el => el.value);
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const preloadHref = await page.$eval('link[rel=preload]', el => el.href);
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const html = await page.$eval('.main-container', el => el.outerHTML);
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```
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If you are using TypeScript, you may have to provide an explicit type to the first argument of the `pageFunction`. By default it is typed as `Element`, but you may need to provide a more specific sub-type:
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## Example 2
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```ts
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// if you don't provide HTMLInputElement here, TS will error
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// as `value` is not on `Element`
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const searchValue = await page.$eval(
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'#search',
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(el: HTMLInputElement) => el.value
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);
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```
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The compiler should be able to infer the return type from the `pageFunction` you provide. If it is unable to, you can use the generic type to tell the compiler what return type you expect from `$eval`:
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## Example 3
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```ts
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// The compiler can infer the return type in this case, but if it can't
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// or if you want to be more explicit, provide it as the generic type.
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const searchValue = await page.$eval<string>(
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'#search',
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(el: HTMLInputElement) => el.value
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);
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```
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