mirror of
https://git.alemi.dev/guestbook.rs.git
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72 lines
3.5 KiB
JavaScript
72 lines
3.5 KiB
JavaScript
/**
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* @typedef GuestbookPage
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* @type {Object}
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* @property {number} id - unique page id
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* @property {string} author - name of page author
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* @property {string} body - main page body
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* @property {string|undefined} contact - optional page author's contact
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* @property {string|undefined} url - optional url to author's contact, if either mail or http link
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* @property {string} avatar - unique hash (based on contact) to use for libravatar img href
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* @property {Date} date - time of creation for page
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* @property
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*/
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/**
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* Hook infinite scroll callback with element builder
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*
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* @param {(data:GuestbookPage)=>string} builder - function invoked to generate new elements, must return HTML string
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* @param {Object} [opt] - configuration options for infinite scroll behavior
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* @param {number} [opt.threshold] - from 0 to 1, percentage of scroll at which new fetch triggers (default 0.9)
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* @param {number} [opt.debounce] - how many milliseconds to wait before processing new scroll events (default 250)
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* @param {string} [opt.container_id] - html id of container element to inject new values into (default '#container')
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* @param {string} [opt.api_url] - url for api calls (default '/api')
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* @param {string} [opt.offset_arg] - how the offset/page argument is called in the api backend (default 'offset')
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* @param {boolean} [opt.prefetch] - load first page immediately, before any scroll event is received (default true)
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* @param {boolean} [opt.free_index] - wether backend api allows free indexing (?offset=17) or expects pagination (?page=1) (default true)
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*
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* @example
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* hookInfiniteScroll(
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* (data) => { return `<li><b>${data.author}</b>: ${data.body}</li>` },
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* {threshold: 0.75, debounce: 1000, api_url: 'http://my.custom.backend/api'}
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* );
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*/
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export default function hookInfiniteScroll(builder, opt) {
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if (opt === undefined) opt = {};
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// we could do it with less lines using || but it checks for truthy (e.g. would discard debounce 0)
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// explicitly check for undefined to avoid this, it's done only once at the start anyway
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let container_id = opt.container_id != undefined ? opt.container_id : "#container";
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let threshold = opt.threshold != undefined ? opt.threshold : 0.9;
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let debounce = opt.debounce != undefined ? opt.debounce : 250;
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let api_url = opt.api_url != undefined ? opt.api_url : "/api";
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let prefetch = opt.prefetch != undefined ? opt.prefetch : true;
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let offset_arg = opt.offset_arg != undefined ? opt.offset_arg : "offset";
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let free_index = opt.free_index != undefined ? opt.free_index : true;
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let container = document.getElementById(container_id);
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let last_activation = Date.now();
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let offset = 0;
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function scrollDepth() {
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let html_tag = document.body.parentElement;
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return html_tag.scrollTop / (html_tag.scrollHeight - html_tag.clientHeight)
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}
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let callback = async (ev) => {
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if (ev !== true && scrollDepth() < threshold) return; // not scrolled enough
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if (ev !== true && Date.now() - last_activation < debounce) return; // triggering too fast
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last_activation = Date.now();
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let response = await fetch(`${api_url}?${offset_arg}=${offset}`);
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let replies = await response.json();
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if (replies.length == 0) {
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// reached end, unregister self
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return document.removeEventListener("scroll", callback);
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}
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offset += free_index ? replies.length : 1; // track how deep we went
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for (let repl of replies) {
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container.innerHTML += builder(repl);
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}
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};
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document.addEventListener("scroll", callback);
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if (prefetch) callback(true); // invoke once immediately
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}
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