| "sourcesContent": ["/**\n * @license\n * Copyright 2024 The Go Authors. All rights reserved.\n * Use of this source code is governed by a BSD-style\n * license that can be found in the LICENSE file.\n */\n\n/**\n * A treeNavController adds dynamic expansion and selection of index list\n * elements based on scroll position.\n *\n * Use it as follows:\n * - Add the .js-Tree class to a parent element of your index and content.\n * - Add the .js-Tree-item class to <li> elements of your index.\n * - Add the .js-Tree-heading class to <hN> heading elements of your content.\n *\n * Then, when you scroll content, the 'aria-selected' and 'aria-expanded'\n * attributes of your tree items will be set according to the current content\n * scroll position. The included treenav.css implements styling to expand and\n * highlight index elements according to these attributes.\n */\nexport function treeNavController(el: HTMLElement) {\n const headings = el.querySelectorAll<HTMLHeadingElement>(\".js-Tree-heading\");\n const callback = () => {\n // Collect heading elements above the scroll position.\n let above: HTMLHeadingElement[] = [];\n for (const h of headings) {\n const rect = h.getBoundingClientRect();\n if (rect.height && rect.top < 80) {\n above.unshift(h);\n }\n }\n // Highlight the first heading even if we're not yet scrolled below it.\n if (above.length == 0 && headings[0] instanceof HTMLHeadingElement) {\n above = [headings[0]];\n }\n // Collect the set of heading levels we're immediately below, at most one\n // per heading level, by decresing level.\n // e.g. [<h3 element>, <h2 element>, <h1 element>]\n let threshold = Infinity;\n const active: HTMLHeadingElement[] = [];\n for (const h of above) {\n const level = Number(h.tagName[1]);\n if (level < threshold) {\n threshold = level;\n active.push(h);\n }\n }\n // Update aria-selected and aria-expanded for all items, per the current\n // position.\n const navItems = el.querySelectorAll<HTMLElement>(\".js-Tree-item\");\n for (const item of navItems) {\n const headingId = item.dataset[\"headingId\"];\n let selected = false,\n expanded = false;\n for (const h of active) {\n if (h.id === headingId) {\n if (h === active[0]) {\n selected = true;\n } else {\n expanded = true;\n }\n break;\n }\n }\n item.setAttribute(\"aria-selected\", selected ? \"true\" : \"false\");\n item.setAttribute(\"aria-expanded\", expanded ? \"true\" : \"false\");\n }\n };\n\n // Update on changes to viewport intersection, defensively debouncing to\n // guard against performance issues.\n const observer = new IntersectionObserver(debounce(callback, 20));\n for (const h of headings) {\n observer.observe(h);\n }\n}\n\nexport function debounce<T extends (...args: unknown[]) => unknown>(\n callback: T,\n wait: number\n) {\n let timeout: number;\n return (...args: unknown[]) => {\n clearTimeout(timeout);\n timeout = setTimeout(() => callback(...args), wait);\n };\n}\n"], |
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| "names": ["treeNavController", "el", "headings", "callback", "above", "h", "rect", "threshold", "active", "level", "navItems", "item", "headingId", "selected", "expanded", "observer", "debounce", "wait", "timeout", "args"] |
