How does Google crawl Javascript web pages?

 JavaScript is currently one of the most widely used programming languages. It is not only supported by most mainstream browsers, but also can see the compilation effect in real time, which is also helpful for user experience.

At Google I/O, Google speaker Tom Greenaway mentioned how Google handles Javascript web pages. The focus here is that Google has different indexing and ranking mechanisms for Javascript web pages and non-Javascript web pages.

(Note: Google I/O, Google’s annual web developer conference, the focus of discussion is to develop web applications using Google and open web technologies.)

 

To be clear, the Google search spider (Googlebot) will search and crawl Javascript webpages in stages. At first, it will search the web content on the server side first, but will delay the Javascript code first, and wait until Googlebot is allocated resources again. Search and index the results of Javascript compiled web pages again. The interval between two searches may be several days.

 

For the above process, we can refer to the figure below:

So if a webpage uses a lot of Javascript to generate content, the content indexed by Google may be different from the content of the current website, and some details may be missing.

 

For example, if Javascript is used to generate news content , the indexed content may be out of date before Google performs a second crawl for Javascript . If there is not much content on the web page during the first crawl, it will have an impact on ranking or traffic.

Assuming that this webpage is newly built, it may take more time to obtain index and ranking weights.

 

From the perspective of SEO, we would recommend that the main content (text, pictures...) be written directly in the web page as much as possible (the first search will be crawled), rather than written in Javascript , To avoid losing traffic during the few days that have not been indexed.