Use FontAwesome icon inside a ::before pseudo element with attr()
Try with Unicode
CSS escape sequences only work within CSS strings. When you take a CSS escape sequence from an HTML attribute (i.e. outside of CSS), it will be read literally, not interpreted as part of a CSS string.
If you want to encode the character within an HTML attribute, you need to encode it as an HTML entity.
you should add "&#x"
before your font-Awesome icon code. ie, if you want to use /f086
, then write 
instead
get the unicode from here - https://fortawesome.github.io/Font-Awesome/cheatsheet/
UPDATE
If you are using fontAwesome 5, change font-family: "FontAwesome";
to font-family: 'Font Awesome 5 Free';
div:before {
content: attr(data-background-icon);
font-family: "FontAwesome";
}
<link href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css" rel="stylesheet"/>
<div data-background-icon=''></div>
CSS reads \f086
as a string and not as an escape sequence. The fix is either to use it directly inside content attribute like content: '\f086';
or directly copying and pasting icon in HTML attribute (make sure you save your file as UTF-8)
HTML:
<div data-background-icon=""></div> <!-- this is the bluetooth icon copied from fontawesome -->
CSS:
div::before {
content: attr(data-background-icon);
font-family: "FontAwesome";
}
OR make use of HTML entities:
HTML:
<div data-background-icon=""></div>
CSS:
div::before {
content: attr(data-background-icon);
font-family: "FontAwesome";
}
Fiddle: https://jsfiddle.net/76v9e2ur/1/