Since you didn’t specify the details, I’m assuming that you are asking about SPA (Single Page Applications) that use Angular.
For SPA’s, if you can get the routing right using Angular routes and also enabling clean routes on the server you are using (ex: .htaccess on Apache), SEO should not get affected.
However there are other things that you need to pay attention to.
Some search engines do not play well with AJAX type page navigation and loading. Since, they don’t see all the data loaded at once, they may index partially loaded webpages (though Google has changed their crawling to accommodate this)
You should also ensure that the meta and other keywords and stuff that search engines like are specific to each page if you want a good SEO. This could be a little challenging when doing SPA’s.
If you do not provide some form of prerendering then yes search engines cannot crawl Angular2 sites (although Google are working on it) as they have no way of telling when the spa has loaded so they will only see the initial page before the SPA has loaded.
To test your site sign up for Google Webmasters and you can use the Search Console to fetch pages and see them as the Google crawler does.
For prerendering options prerender.io is a good SaaS option which is easy to integrate. Also for Angular 2 you can use Angular Universal for server side rendering, but it is still at an early stage so not that stable.
For more information this Angular Connect talk on SEO best practises is worth a watch.
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Since you didn’t specify the details, I’m assuming that you are asking about SPA (Single Page Applications) that use Angular.
For SPA’s, if you can get the routing right using Angular routes and also enabling clean routes on the server you are using (ex: .htaccess on Apache), SEO should not get affected.
However there are other things that you need to pay attention to.
Some search engines do not play well with AJAX type page navigation and loading. Since, they don’t see all the data loaded at once, they may index partially loaded webpages (though Google has changed their crawling to accommodate this)
You should also ensure that the meta and other keywords and stuff that search engines like are specific to each page if you want a good SEO. This could be a little challenging when doing SPA’s.
If you do not provide some form of prerendering then yes search engines cannot crawl Angular2 sites (although Google are working on it) as they have no way of telling when the spa has loaded so they will only see the initial page before the SPA has loaded.
To test your site sign up for Google Webmasters and you can use the Search Console to fetch pages and see them as the Google crawler does.
For prerendering options prerender.io is a good SaaS option which is easy to integrate. Also for Angular 2 you can use Angular Universal for server side rendering, but it is still at an early stage so not that stable.
For more information this Angular Connect talk on SEO best practises is worth a watch.