puppeteer/docs/api/puppeteer.webworker.evaluate.md

---
sidebar_label: WebWorker.evaluate
---

# WebWorker.evaluate() method

Evaluates a given function in the [worker](./puppeteer.webworker.md).

#### Signature:

```typescript
class WebWorker {
  evaluate<
    Params extends unknown[],
    Func extends EvaluateFunc<Params> = EvaluateFunc<Params>,
  >(func: Func | string, ...args: Params): Promise<Awaited<ReturnType<Func>>>;
}
```

## Parameters

| Parameter | Type           | Description                               |
| --------- | -------------- | ----------------------------------------- |
| func      | Func \| string | Function to be evaluated.                 |
| args      | Params         | Arguments to pass into <code>func</code>. |

**Returns:**

Promise&lt;Awaited&lt;ReturnType&lt;Func&gt;&gt;&gt;

The result of `func`.

## Remarks

If the given function returns a promise, [evaluate](./puppeteer.webworker.evaluate.md) will wait for the promise to resolve.

As a rule of thumb, if the return value of the given function is more complicated than a JSON object (e.g. most classes), then [evaluate](./puppeteer.webworker.evaluate.md) will \_likely\_ return some truncated value (or `{}`). This is because we are not returning the actual return value, but a deserialized version as a result of transferring the return value through a protocol to Puppeteer.

In general, you should use [evaluateHandle](./puppeteer.webworker.evaluatehandle.md) if [evaluate](./puppeteer.webworker.evaluate.md) cannot serialize the return value properly or you need a mutable [handle](./puppeteer.jshandle.md) to the return object.