Cannot Save Source Text in Preset Adobe After Effect

I'a trying to save a simple number animatiion with this code: 

num = ""+ effect("Angle Control")("Angle").value.toFixed(0) + "";

function addCommas(x) {
return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

addCommas(num)

but i cannot save it as an animation preset in adobe after effect, while on the video i just watched th guy was able to... Any idea oabout how to fix the porblem ? 

link of vieo: https://www.youtube.com/watch?v=KYweBo9lgKM