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