"Several research has shown that continuously staring at a laptop for long periods — an unavoidable part of reading digital books — can worsen the..."

[hardyweineberg]

"Several research has shown that continuously staring at a laptop for long periods — an unavoidable part of reading digital books — can worsen the eyesight of people who are short-sighted or long-sighted ."
Source: me

Did I use the em dashes grammatically and correctly?

 

[probus]

The dashes are fine, but research is an uncountable noun and therefore several is incorrect. You could say instead a good deal of research or several researchers.

 

[tedmc]

Should there be a space before and after an em dash?

 

[hardyweineberg]

Should there be a space before and after an em dash?

You can put or decide not to; both are correct.

 

[5jj]

Spacing around an em dash varies. Most newspapers insert a space before and after the dash, and many popular magazines do the same, but most books and journals omit spacing, closing whatever comes before and after the em dash right up next to it.

How to Use Em Dashes (—), En Dashes (–) , and Hyphens (-)

Be dashing—and do it well

www.merriam-webster.com

 

[tedmc]

You can put or decide not to; both are correct.

So the spacing is optional. Visually, I think the clause stands out better with the spacing, which is what is intended.

 

[emsr2d2]

I use a space at each end of an em dash. Without the spaces, there's still a chance a reader might mistake it for a hyphen.