Firefox preload polyfill for Link headers

gistfile1.js

// https://gist.github.com/yoavweiss/b1f798bb2be4e671107b#file-preload_feature_detection-js
const supportsPreload = (function() {
    try {
        return document.createElement("link").relList.supports('preload');
    } catch (e) {
        return false;
    }
}());
if (supportsPreload) {
    console.log("Supports preload");
}else{
    fetch(window.location, {
        method: "HEAD"
    }).then(x => {
        const headers=Array.from(x.headers).filter(x=>x[0]==="link").map(x=>x[1]);
        headers.forEach(header=>{
            const file=/^<([^>]+)>/.exec(header)[1];
            fetch(file);
        })
    });
}