Function isStyleRule

src/inject/dynamic-theme/css-rules.ts:183–197

(rule: CSSRule | null)

const layerRules = new WeakSet<CSSRule>();

export function isStyleRule(rule: CSSRule | null): rule is CSSStyleRule {
    if (!rule) {
        return false;
    }
    if (styleRules.has(rule)) {
        return true;
    }
    // Duck typing is faster than instanceof
    // https://jsben.ch/B0eLa
    if ((rule as CSSStyleRule).selectorText) {
        styleRules.add(rule);
        return true;
    }
    return false;
}

export function isImportRule(rule: CSSRule | null): rule is CSSImportRule {
    if (!rule) {