`—` or `—` is there any difference in HTML output?

Question

— or —

Is there a difference between these? Is one better-supported than the other?

Answer 1

— :: — :: \u2014

When representing the m-dash in a JavaScript text string for output to HTML, note that it will be represented by its unicode value. There are cases when ampersand characters ('&') will not be resolved—notably certain contexts within JSX. In this case, neither — nor — will work. Instead you need to use the Unicode escape sequence: \u2014.

For example, when implementing a render() method to output text from a JavaScript variable:

render() {
   let text='JSX transcoders will preserve the & character—to ' 
            + 'protect from possible script hacking and cross-site hacks.'
   return (
     
{text}
   )
}

This will output:

JSX transcoders will preserve the & character—to protect from possible script hacking and cross-site hacks.

Instead of the &– prefixed representation, you should use \u2014:

let text='JSX transcoders will preserve the & character\u2014to …'