How to make a custom LinkedIn share button

Official LinkedIn API for sharing:

https://developer.linkedin.com/docs/share-on-linkedin

Read Terms of Use!

Example link using "Customized URL" method: http://www.linkedin.com/shareArticle?mini=true&url=https://stackoverflow.com/questions/10713542/how-to-make-custom-linkedin-share-button/10737122&title=How%20to%20make%20custom%20linkedin%20share%20button&summary=some%20summary%20if%20you%20want&source=stackoverflow.com

You just need to open it in popup using JavaScript or load it to iframe. Simple and works - that's what I was looking for!

EDIT: Video attached to a post:

I checked that you can't really embed any video to LinkedIn post, the only option is to add the link to the page with video itself.

You can achieve it by putting YT link into url param:

https://www.linkedin.com/shareArticle?mini=true&url=https://www.youtube.com/watch?v=SBi92AOSW2E

If you specify summary and title then LinkedIn will stop pulling it from the video, e.g.:

https://www.linkedin.com/shareArticle?mini=true&summary=youtube&title=f1&url=https://www.youtube.com/watch?v=SBi92AOSW2E

It does work exactly the same with Vimeo, and probably will work for any website. Hope it will help.

EDIT 2: Pulling images to the post:

When you open above links you will see that LinkedIn loads some images along with the passed URL (and optionally title and summary).

LinkedIn does it automatically, and you can read about it here: https://developer.linkedin.com/docs/share-on-linkedin#opengraph

It's interesting though as it says:

If Open Graph tags are present, LinkedIn's crawler will not have to rely on it's own analysis to determine what content will be shared, which improves the likelihood that the information that is shared is exactly what you intended.

It tells me that even if Open Graph information is not attached, LinkedIn can pull this data based on its own analysis. And in case of YouTube it seems to be the case, as I couldn't find any Open Graph tags added to YouTube pages.

You can make your own sharing button using the LinkedIn ShareArticle URL, which can have the following parameters:

https://www.linkedin.com/shareArticle?mini=true&url={articleUrl}&title={articleTitle}&summary={articleSummary}&source={articleSource}

You can find the documentation here, just choose "Customized URL" to see the details.