Should I use spaces around an em-dash?
An em-dash is a punctuation mark which is used alone to indicate a pause in speech or in pairs to take the place of commas. The name comes from the fact that, in tradtional typesetting, the dash is the same width as a capital M.
Most writers (and style guides) use the em-dash without spaces on either side.
He was travelling very quickly—the trees were a blur through the window—but the train showed no sign of slowing down.
Most newspapers, however, follow the AP style guide, which recommends a space on either side. This is because newspaper columns are narrow and having the spaces helps with the layout of the text.
Her speech on the economy — delivered in front of a crowd of 10,000 supporters — was the highlight of the conference.
So, we suggest that you choose which style to follow depending upon the type of writing. The most important thing is to be consistent!