@applitools/dom-snapshot

dom-snapshot

Script for extracting resources and DOM in CDT format, to serve as the input for rendering a screenshot with the visual grid.

Installing

npm install @applitools/dom-snapshot

Usage

From Node.js

This package exports functions that can be used when working with puppeteer, CDP or Selenium in Node.js:

• getProcessPage
• getProcessPagePoll
• getPollResult

The following methods are deprecated:

• getProcessPageAndSerialize
• getProcessPageAndSerializePoll

These async functions return a string with a function that can be sent to the browser for evaluation. It doesn't immediately invoke the function, so the sender should wrap it as an IIFE. For example:

const {getProcessPage} = require('@applitools/dom-snapshot');
const processPage = await getProcessPage();
const returnValue = await page.evaluate(`(${processPage})()`); // puppeteer

From the browser

By using the non bundled version of the scripts:

• src/browser/processPage
• src/browser/processPageAndSerialize (deprecated)

These functions can then be bundled together with other client-side code so they are consumed regardless of a browser driver (this is how the Eyes.Cypress SDK uses it).

From non-JavaScript code

This package's dist folder contains scripts that can be sent to the browser regradless of driver and language. An agent that wishes to extract information from a webpage can read the contents of dist/processPage and send that to the browser as an async script. There's still the need to wrap it in a way that invokes it.

For example in Java with Selenium WebDriver:

  String response = driver.executeAsyncScript("const callback = arguments[arguments.length - 1];(" + processPage + ")().then(JSON.stringify).then(callback, function(err) {callback(err.stack || err.toString())})";

Note for Selenium WebDriver users: The return value must not include objects with the property nodeType. Browser drivers interpret those as HTML nodes, and thus corrupt the result. A possible remedy to this is to JSON.stringify the result before sending it back to the calling process. That's what we're doing in the example above.

The processPage script

Arguments

One single argument with the following properties:

processPage({
  doc = document,
  showLogs,
  useSessionCache,
  dontFetchResources,
  fetchTimeout,
  skipResources,
  compressResources,
  serializeResources,
})

• doc - the document for which to take a snapshot. Default: the current document.
• showLogs - toggle verbose logging in the console
• useSessionCache - cache resources in the browser's sessionCache. Optimization for cases where processPage is run on the same browser tab more than once.
• dontFetchResources - dont fetch resources. Only return resourceUrls and not blobs.
• fetchTimeout - the time it takes to fail on a hanging fetch request for getting a resource. Default: 10000 (10 seconds)
• skipResources - an array of absolute URL's of resources which shouldn't be fetched by processPage.
• compressResources - a boolean indicating whether to use the deflate algorithm on blob data in order to return a smaller response. The caller should then inflate the blobs to get the value.
• serializeResources - a boolean indicating whether to return blob data as base64 strings. This is useful in most cases since the processPage function is generally run from outside the browser, so its response should be serializable.

Return value

This script receives a document, and returns an object with the following:

• url - the URL of the document.
• cdt - a flat array representing the document's DOM in CDT format.
• resourceUrls - an array of strings with URL's of resources that appear in the page's DOM or are referenced from a CSS resource but are cross-origin and therefore could not be fetched from the browser.
• blobs - an array of objects with the following structure: {url, type, value}. These are resources that the browser was able to fetch. The type property is the Content-Type response header. The value property contains an ArrayBuffer with the content of the resource.
• frames: an array with objects which recursively have the same structure as the processPage return value: {url, cdt, resourceUrls, blobs, frames}.
• srcAttr - for frames, this is the original src attribute on the frame (in use by Selenium IDE Eyes extension)
• crossFrames - an array of objects with the following structure: {selector, index}. The selector field has a value of css selector (strings) that point to cross origin frames. The index is an index (number) of frame node in a cdt array, this could be useful to override src attribute once dom snapshot is taken. The caller can then call processPage in the context of those frames in order to build a complete DOM snapshot which also contains cross origin iframes.
• selector - a css selector (string) for the frame (only for iframes). This is helpful to construct the full frame chain that leads to cross origin iframes on the caller side.

The script scans the DOM for resource references, fetches them, and then also scans the body of css resources for more references, and so on recursively.

processPagePoll

This function calls processPage and returns immediately. Then pollResult should be called (or any of the ...Poll script variations, for backwards compatibility) to get the polling result.

Arguments

This function accepts the same arguments as processPage, with one additional parameter:

• chunkByteLength - this will cause additional polling after the snapshot is ready, and will transfer the result in chunks, with the chunk size specified. Default: undefined.

For example, to pass a maximum chunk size of 256MB:

procesPagePoll({chunkByteLength: 1024 * 1024 * 256})

Return value

The polling result is a stringified JSON object, which is of the following shape:

{
  status: string,
  error: string,
  value: object
}

Status could be one of:

• "SUCCESS" - there's a value field with the return value
• "ERROR" - there's an error field with the result
• "WIP" - internal status, handled by pollResult to continue polling until "SUCCESS" or "ERROR" are received.
• "SUCCESS_CHUNKED" - internal status, handled by pollResult to continue polling until the entire value is received (used with chunkByteLength).

pollResult

returns the poll result - an object with the same shape as processPagePoll.