75 lines
7.5 KiB
TypeScript
75 lines
7.5 KiB
TypeScript
/** Runs inside the browser against static DOM and resolved CSS, without executing page scripts. */
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export function inspectDocument(options: { kind: "accessible" | "overflow"; ignore: string[]; disclosures: boolean }) {
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const { document, getComputedStyle, innerWidth } = globalThis as any;
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const findings: { rule: string; selector: string; severity: "error" | "warning" | "review"; message: string; evidence: Record<string, unknown> }[] = [];
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const elements = [...document.querySelectorAll("body *")];
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if (options.disclosures) for (const element of elements) if (element.tagName === "DETAILS") element.open = true;
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const selector = (node: any): string => {
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if (node.id) return `[id=${JSON.stringify(node.id)}]`;
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const parts: string[] = [];
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while (node && node.tagName !== "BODY") {
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const index = [...node.parentElement.children].indexOf(node) + 1;
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parts.unshift(`${node.tagName.toLowerCase()}:nth-child(${index})`);
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node = node.parentElement;
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}
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return `body > ${parts.join(" > ")}`;
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};
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const add = (node: any, rule: string, message: string, evidence: Record<string, unknown> = {}, severity: "error" | "warning" | "review" = "error") => findings.push({ selector: selector(node), rule, message, evidence, severity });
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const canvas = document.createElement("canvas"); canvas.width = canvas.height = 1;
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const ctx = canvas.getContext("2d", { willReadFrequently: true });
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const color = (value: string): number[] => { ctx.clearRect(0, 0, 1, 1); ctx.fillStyle = value; ctx.fillRect(0, 0, 1, 1); return [...ctx.getImageData(0, 0, 1, 1).data]; };
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const composite = (front: number[], back: number[]): number[] => front.slice(0, 3).map((channel, index) => channel * front[3]! / 255 + back[index]! * (1 - front[3]! / 255)).concat(255);
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const luminance = (rgb: number[]): number => rgb.slice(0, 3).map((value) => { const c = value / 255; return c <= .04045 ? c / 12.92 : ((c + .055) / 1.055) ** 2.4; }).reduce((sum, value, index) => sum + value * [.2126, .7152, .0722][index]!, 0);
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let checked = 0;
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for (const node of elements) {
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if (options.ignore.some((ignore) => node.closest(ignore))) continue;
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const style = getComputedStyle(node);
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const box = node.getBoundingClientRect();
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if (!box.width || !box.height || style.display === "none" || style.visibility !== "visible" || node.closest("[hidden], [inert]")) continue;
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checked++;
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if (options.kind === "overflow") {
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const clippedX = ["hidden", "clip"].includes(style.overflowX) && node.scrollWidth > node.clientWidth + 1;
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const clippedY = ["hidden", "clip"].includes(style.overflowY) && node.scrollHeight > node.clientHeight + 1;
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const truncated = style.textOverflow === "ellipsis" || (style.webkitLineClamp !== "none" && Number(style.webkitLineClamp) > 0);
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if ((clippedX || clippedY) && !truncated) add(node, "clipping", "Content exceeds a clipping boundary", { overflowX: style.overflowX, overflowY: style.overflowY, clientWidth: node.clientWidth, scrollWidth: node.scrollWidth, clientHeight: node.clientHeight, scrollHeight: node.scrollHeight });
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let managed = false;
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for (let parent = node.parentElement; parent; parent = parent.parentElement) if (["auto", "scroll", "hidden", "clip"].includes(getComputedStyle(parent).overflowX)) { managed = true; break; }
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if (!managed && (box.right > innerWidth + 1 || box.left < -1)) add(node, "viewport-overflow", "Element extends outside the viewport without a containing scroll region", { left: box.left, right: box.right, viewportWidth: innerWidth });
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continue;
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}
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const label = node.getAttribute("aria-label") || (node.getAttribute("aria-labelledby") || "").split(/\s+/).map((id: string) => document.getElementById(id)?.textContent || "").join("").trim() || [...(node.labels || [])].map((label: any) => label.textContent).join("").trim();
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for (const id of (node.getAttribute("aria-labelledby") || "").split(/\s+/).filter(Boolean)) if (!document.getElementById(id)) add(node, "aria-reference", "aria-labelledby references a missing element", { id });
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if (["A", "BUTTON", "INPUT", "SELECT"].includes(node.tagName) && !node.disabled && (box.width < 24 || box.height < 24)) add(node, "target-size", "Interactive target is smaller than 24 CSS pixels; spacing exceptions require review", { width: box.width, height: box.height }, "review");
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if (node.tagName === "IMG" && !node.hasAttribute("alt")) add(node, "image-alt", "Image lacks an alt attribute");
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if (["INPUT", "SELECT", "TEXTAREA"].includes(node.tagName) && !["hidden", "submit", "button", "reset"].includes(node.type) && !label) add(node, "control-name", "Form control lacks a programmatic label");
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if (["A", "BUTTON"].includes(node.tagName) && !label && !node.textContent.trim() && !node.querySelector("img[alt]")) add(node, "control-name", "Interactive element lacks an accessible name");
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const ownText = [...node.childNodes].some((child: any) => child.nodeType === 3 && child.textContent.trim());
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if (!ownText) continue;
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const chain: any[] = []; let opacity = 1;
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for (let parent = node; parent; parent = parent.parentElement) { chain.unshift(parent); opacity *= Number(getComputedStyle(parent).opacity); }
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let background = [255, 255, 255, 255];
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const effects: Record<string, unknown>[] = [];
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for (const parent of chain) {
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const css = getComputedStyle(parent);
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background = composite(color(css.backgroundColor), background);
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if (css.filter !== "none" || css.backdropFilter !== "none" || css.mixBlendMode !== "normal" || css.backgroundImage !== "none" || css.clipPath !== "none" || css.maskImage !== "none") effects.push({ selector: selector(parent), filter: css.filter, backdropFilter: css.backdropFilter, blend: css.mixBlendMode, backgroundImage: css.backgroundImage, clipPath: css.clipPath, maskImage: css.maskImage });
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}
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const foreground = color(style.color); foreground[3] = foreground[3]! * opacity;
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const text = composite(foreground, background);
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const l1 = luminance(text), l2 = luminance(background);
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const contrast = (Math.max(l1, l2) + .05) / (Math.min(l1, l2) + .05);
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const threshold = parseFloat(style.fontSize) >= 24 || (parseFloat(style.fontSize) >= 18.667 && Number(style.fontWeight) >= 700) ? 3 : 4.5;
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if (effects.length) add(node, "visibility-effects", "Filters, backdrop effects or masking require pixel-level review; nominal contrast is not conclusive", { effects, opacity, nominalContrast: contrast }, "review");
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if (contrast < threshold) add(node, "text-contrast", "Estimated text contrast falls below the configured text threshold", { contrast, threshold, opacity, estimate: effects.length > 0 }, effects.length ? "review" : "error");
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if (opacity < .5) add(node, "low-opacity", "Effective ancestor opacity reduces text visibility", { opacity }, "warning");
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}
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if (options.kind === "accessible") {
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const ids = new Set<string>();
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for (const node of document.querySelectorAll("[id]")) { if (ids.has(node.id)) add(node, "duplicate-id", "Duplicate identifiers make references ambiguous", { id: node.id }); ids.add(node.id); }
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let previous = 0;
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for (const heading of document.querySelectorAll("h1,h2,h3,h4,h5,h6")) { const level = Number(heading.tagName.slice(1)); if (previous && level > previous + 1) add(heading, "heading-order", "Heading hierarchy skips a level", { previous, level }, "warning"); previous = level; }
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if (!document.documentElement.lang) findings.push({ selector: "html", rule: "document-language", severity: "error", message: "Document language is missing", evidence: {} });
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if (!document.title.trim()) findings.push({ selector: "head", rule: "document-title", severity: "error", message: "Document title is missing", evidence: {} });
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}
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return { findings, checked };
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}
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