CSS: set font weight depending on fallback font

Question

I am trying to set the font-weight for an element based on the font that gets chosen. For example, I may be trying to do something like this:

h1 {
    font-f         


        

Answer 1

Won't this work? Untested.

<style>
@font-face {
    font-family: "ArialBold";
    src: local("Arial Narrow");
    font-weight: bold;
}
@font-face {
    font-family: "ImpactNormal";
    src: local("Impact");
    font-weight: normal;
}
@font-face {
    font-family: "SansSerifBold";
    src: local("sans-serif");
    font-weight: bold;
}
h1 {
    font-family: ArialBold, ImpactNormal, SansSerifBold;
}
</style>

Answer 2

I'm 99.99999% sure this can't be done without some serious JavaScript magic, and even with JavaScript it's damn difficult to find out which font was used in the end.

Related: get computed font-family in JavaScript asked by yours truly