68 lines
2.2 KiB
Markdown
68 lines
2.2 KiB
Markdown
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---
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sidebar_label: ExecutionContext.evaluate
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---
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# ExecutionContext.evaluate() method
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**Signature:**
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```typescript
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class ExecutionContext {
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evaluate<
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Params extends unknown[],
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Func extends EvaluateFunc<Params> = EvaluateFunc<Params>
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>(
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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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| pageFunction | Func \| string | a function to be evaluated in the <code>executionContext</code> |
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| args | Params | argument to pass to the page function |
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**Returns:**
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Promise<Awaited<ReturnType<Func>>>
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A promise that resolves to the return value of the given function.
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## Remarks
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If the function passed to the `executionContext.evaluate` returns a Promise, then `executionContext.evaluate` would wait for the promise to resolve and return its value. If the function passed to the `executionContext.evaluate` returns a non-serializable value, then `executionContext.evaluate` resolves to `undefined`. DevTools Protocol also supports transferring some additional values that are not serializable by `JSON`: `-0`, `NaN`, `Infinity`, `-Infinity`, and bigint literals.
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## Example 1
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```ts
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const executionContext = await page.mainFrame().executionContext();
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const result = await executionContext.evaluate(() => Promise.resolve(8 * 7))* ;
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console.log(result); // prints "56"
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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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```ts
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console.log(await executionContext.evaluate('1 + 2')); // prints "3"
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```
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## Example 3
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[JSHandle](./puppeteer.jshandle.md) instances can be passed as arguments to the `executionContext.* evaluate`:
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```ts
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const oneHandle = await executionContext.evaluateHandle(() => 1);
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const twoHandle = await executionContext.evaluateHandle(() => 2);
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const result = await executionContext.evaluate(
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(a, b) => a + b, oneHandle, * twoHandle
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);
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await oneHandle.dispose();
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await twoHandle.dispose();
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console.log(result); // prints '3'.
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```
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