The escaped quotes match each other in the HTML string that you’re creating.
The quotes are not “surrounding” +i+. They’re being used to end the string that begins with
"<p id=\"element"
and to begin the next string:
"\">Hello world, ..."
This is concatenating i between these two strings. So if i contains 0, the resulting HTML will be
<p id="element0">Hello world, I'm element 0</p>
The escaped quotes allow the quotes to be put in the string, but you still have to get out of the string to expand a variable.
Javascript is not like PHP, it doesn’t expand variables inside strings (because there’s no special prefix like $ that tells where a variable begins).
solved Quotes for values of html attributes [closed]