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Version: 3.4

BasicCrawler <Context>

Provides a simple framework for parallel crawling of web pages. The URLs to crawl are fed either from a static list of URLs or from a dynamic queue of URLs enabling recursive crawling of websites.

BasicCrawler is a low-level tool that requires the user to implement the page download and data extraction functionality themselves. If we want a crawler that already facilitates this functionality, we should consider using CheerioCrawler, PuppeteerCrawler or PlaywrightCrawler.

BasicCrawler invokes the user-provided requestHandler for each Request object, which represents a single URL to crawl. The Request objects are fed from the RequestList or RequestQueue instances provided by the requestList or requestQueue constructor options, respectively. If neither requestList nor requestQueue options are provided, the crawler will open the default request queue either when the crawler.addRequests() function is called, or if requests parameter (representing the initial requests) of the crawler.run() function is provided.

If both requestList and requestQueue options are used, the instance first processes URLs from the RequestList and automatically enqueues all of them to the RequestQueue before it starts their processing. This ensures that a single URL is not crawled multiple times.

The crawler finishes if there are no more Request objects to crawl.

New requests are only dispatched when there is enough free CPU and memory available, using the functionality provided by the AutoscaledPool class. All AutoscaledPool configuration options can be passed to the autoscaledPoolOptions parameter of the BasicCrawler constructor. For user convenience, the minConcurrency and maxConcurrency options of the underlying AutoscaledPool constructor are available directly in the BasicCrawler constructor.

Example usage:

import { BasicCrawler, Dataset } from 'crawlee';

// Create a crawler instance
const crawler = new BasicCrawler({
    async requestHandler({ request, sendRequest }) {
        // 'request' contains an instance of the Request class
        // Here we simply fetch the HTML of the page and store it to a dataset
        const { body } = await sendRequest({
            url: request.url,
            method: request.method,
            body: request.payload,
            headers: request.headers,
        });

        await Dataset.pushData({
            url: request.url,
            html: body,
        })
    },
});

// Enqueue the initial requests and run the crawler
await crawler.run([
    'http://www.example.com/page-1',
    'http://www.example.com/page-2',
]);

Hierarchy

Index

Constructors

Properties

Methods

Constructors

constructor

Properties

optionalautoscaledPool

autoscaledPool?: AutoscaledPool

A reference to the underlying AutoscaledPool class that manages the concurrency of the crawler.

NOTE: This property is only initialized after calling the crawler.run() function. We can use it to change the concurrency settings on the fly, to pause the crawler by calling autoscaledPool.pause() or to abort it by calling autoscaledPool.abort().

readonlyconfig

config: Configuration = ...

optionalrequestList

requestList?: RequestList

A reference to the underlying RequestList class that manages the crawler's requests. Only available if used by the crawler.

optionalrequestQueue

requestQueue?: RequestQueue

Dynamic queue of URLs to be processed. This is useful for recursive crawling of websites. A reference to the underlying RequestQueue class that manages the crawler's requests. Only available if used by the crawler.

readonlyrouter

router: RouterHandler<Context> = ...

Default Router instance that will be used if we don't specify any requestHandler. See router.addHandler() and router.addDefaultHandler().

optionalrunning

running?: boolean

optionalsessionPool

sessionPool?: SessionPool

A reference to the underlying SessionPool class that manages the crawler's sessions. Only available if used by the crawler.

readonlystats

stats: Statistics

A reference to the underlying Statistics class that collects and logs run statistics for requests.

Methods

addRequests

getRequestQueue

run

  • Runs the crawler. Returns a promise that gets resolved once all the requests are processed. We can use the requests parameter to enqueue the initial requests - it is a shortcut for running crawler.addRequests() before the crawler.run().

    Parameters

    Returns Promise<FinalStatistics>

useState

  • useState<State>(defaultValue?: State): Promise<State>

  • Type parameters

    • State: Dictionary = Dictionary

    Parameters

    • defaultValue: State = ...

    Returns Promise<State>

Page Options