mirror of
https://github.com/puppeteer/puppeteer
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8370ec88ae
This change started as a small change to pull types from DefinitelyTyped over to
Puppeteer for the `evaluateHandle` function but instead ended up also fixing
what looks to be a long standing issue with our existing documentation.
`evaluateHandle` can in fact return an `ElementHandle` rather than a `JSHandle`.
Note that `ElementHandle` extends `JSHandle` so whilst the docs are technically
correct (all ElementHandles are JSHandles) it's confusing because JSHandles
don't have methods like `click` on them, but ElementHandles do.
if you return something that is an HTML element:
```
const button = page.evaluateHandle(() => document.querySelector('button'));
// this is an ElementHandle, not a JSHandle
```
Therefore I've updated the original docs and added a large explanation to the
TSDoc for `page.evaluateHandle`.
In TypeScript land we'll assume the function will return a `JSHandle` but you
can tell TS otherwise via the generic argument, which can only be `JSHandle`
(the default) or `ElementHandle`:
```
const button = page.evaluateHandle<ElementHandle>(() => document.querySelector('button'));
```
63 lines
2.2 KiB
Markdown
63 lines
2.2 KiB
Markdown
<!-- Do not edit this file. It is automatically generated by API Documenter. -->
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[Home](./index.md) > [puppeteer](./puppeteer.md) > [ExecutionContext](./puppeteer.executioncontext.md) > [evaluateHandle](./puppeteer.executioncontext.evaluatehandle.md)
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## ExecutionContext.evaluateHandle() method
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<b>Signature:</b>
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```typescript
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evaluateHandle<HandleType extends JSHandle | ElementHandle = JSHandle>(pageFunction: EvaluateHandleFn, ...args: SerializableOrJSHandle[]): Promise<HandleType>;
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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 | [EvaluateHandleFn](./puppeteer.evaluatehandlefn.md) | a function to be evaluated in the <code>executionContext</code> |
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| args | [SerializableOrJSHandle](./puppeteer.serializableorjshandle.md)<!-- -->\[\] | argument to pass to the page function |
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<b>Returns:</b>
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Promise<HandleType>
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A promise that resolves to the return value of the given function as an in-page object (a [JSHandle](./puppeteer.jshandle.md)<!-- -->).
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## Remarks
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The only difference between `executionContext.evaluate` and `executionContext.evaluateHandle` is that `executionContext.evaluateHandle` returns an in-page object (a [JSHandle](./puppeteer.jshandle.md)<!-- -->). If the function passed to the `executionContext.evaluateHandle` returns a Promise, then `executionContext.evaluateHandle` would wait for the promise to resolve and return its value.
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## Example 1
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```js
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const context = await page.mainFrame().executionContext();
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const aHandle = await context.evaluateHandle(() => Promise.resolve(self));
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aHandle; // Handle for the global object.
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```
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## Example 2
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A string can also be passed in instead of a function.
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```js
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// Handle for the '3' * object.
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const aHandle = await context.evaluateHandle('1 + 2');
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```
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## Example 3
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JSHandle instances can be passed as arguments to the `executionContext.* evaluateHandle`<!-- -->:
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```js
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const aHandle = await context.evaluateHandle(() => document.body);
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const resultHandle = await context.evaluateHandle(body => body.innerHTML, * aHandle);
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console.log(await resultHandle.jsonValue()); // prints body's innerHTML
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await aHandle.dispose();
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await resultHandle.dispose();
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```
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