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Preload feature detection
var DOMTokenListSupports = function(tokenList, token) {
if (!tokenList || !tokenList.supports) {
return;
}
try {
return tokenList.supports(token);
} catch (e) {
if (e instanceof TypeError) {
console.log("The DOMTokenList doesn't have a supported tokens list");
} else {
console.error("That shouldn't have happened");
}
}
};
var linkSupportsPreload = DOMTokenListSupports(document.createElement("link").relList, "preload");
if (!linkSupportsPreload) {
// Dynamically load the things that relied on preload.
}
@triblondon

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commented Jun 30, 2016

If you wanted to reduce the code bloat for production, would this do?

var supportsPreload = (function() { try { document.createElement("link").relList.supports('preload'); return 1 } catch(e) { return 0; }}());
@lsuchanek

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commented Mar 7, 2018

@triblondon I think, better solution is: var supportsPreload = (function() { try { return document.createElement("link").relList.supports('preload'); } catch(e) { return false; }}());
https://github.com/filamentgroup/loadCSS/blob/master/src/cssrelpreload.js

Your code return false positive for FF 58.

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