lemmy/ui/src/utils.ts

951 lines
25 KiB
TypeScript
Vendored

import 'moment/locale/es';
import 'moment/locale/el';
import 'moment/locale/eu';
import 'moment/locale/eo';
import 'moment/locale/de';
import 'moment/locale/zh-cn';
import 'moment/locale/fr';
import 'moment/locale/sv';
import 'moment/locale/ru';
import 'moment/locale/nl';
import 'moment/locale/it';
import 'moment/locale/fi';
import 'moment/locale/ca';
import 'moment/locale/fa';
import 'moment/locale/pl';
import 'moment/locale/pt-br';
import 'moment/locale/ja';
import 'moment/locale/ka';
import 'moment/locale/hi';
import 'moment/locale/gl';
import 'moment/locale/tr';
import 'moment/locale/hu';
import 'moment/locale/uk';
import {
UserOperation,
Comment,
CommentNode as CommentNodeI,
Post,
PrivateMessage,
User,
SortType,
CommentSortType,
ListingType,
DataType,
SearchType,
WebSocketResponse,
WebSocketJsonResponse,
SearchForm,
SearchResponse,
CommentResponse,
PostResponse,
} from './interfaces';
import { UserService, WebSocketService } from './services';
import Tribute from 'tributejs/src/Tribute.js';
import markdown_it from 'markdown-it';
import markdownitEmoji from 'markdown-it-emoji/light';
import markdown_it_container from 'markdown-it-container';
import twemoji from 'twemoji';
import emojiShortName from 'emoji-short-name';
import Toastify from 'toastify-js';
import tippy from 'tippy.js';
import EmojiButton from '@joeattardi/emoji-button';
export const repoUrl = 'https://github.com/LemmyNet/lemmy';
export const helpGuideUrl = '/docs/about_guide.html';
export const markdownHelpUrl = `${helpGuideUrl}#markdown-guide`;
export const sortingHelpUrl = `${helpGuideUrl}#sorting`;
export const archiveUrl = 'https://archive.is';
export const postRefetchSeconds: number = 60 * 1000;
export const fetchLimit: number = 20;
export const mentionDropdownFetchLimit = 10;
export const languages = [
{ code: 'ca', name: 'Català' },
{ code: 'en', name: 'English' },
{ code: 'el', name: 'Ελληνικά' },
{ code: 'eu', name: 'Euskara' },
{ code: 'eo', name: 'Esperanto' },
{ code: 'es', name: 'Español' },
{ code: 'de', name: 'Deutsch' },
{ code: 'gl', name: 'Galego' },
{ code: 'hu', name: 'Magyar Nyelv' },
{ code: 'ka', name: 'ქართული ენა' },
{ code: 'hi', name: 'मानक हिन्दी' },
{ code: 'fa', name: 'فارسی' },
{ code: 'ja', name: '日本語' },
{ code: 'pl', name: 'Polski' },
{ code: 'pt_BR', name: 'Português Brasileiro' },
{ code: 'zh', name: '中文' },
{ code: 'fi', name: 'Suomi' },
{ code: 'fr', name: 'Français' },
{ code: 'sv', name: 'Svenska' },
{ code: 'tr', name: 'Türkçe' },
{ code: 'uk', name: 'українська мова' },
{ code: 'ru', name: 'Русский' },
{ code: 'nl', name: 'Nederlands' },
{ code: 'it', name: 'Italiano' },
];
export const themes = [
'litera',
'materia',
'minty',
'solar',
'united',
'cyborg',
'darkly',
'journal',
'sketchy',
'vaporwave',
'vaporwave-dark',
'i386',
'litely',
];
export const emojiPicker = new EmojiButton({
// Use the emojiShortName from native
style: 'twemoji',
theme: 'dark',
position: 'auto-start',
// TODO i18n
});
const DEFAULT_ALPHABET =
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
function getRandomCharFromAlphabet(alphabet: string): string {
return alphabet.charAt(Math.floor(Math.random() * alphabet.length));
}
export function randomStr(
idDesiredLength: number = 20,
alphabet = DEFAULT_ALPHABET
): string {
/**
* Create n-long array and map it to random chars from given alphabet.
* Then join individual chars as string
*/
return Array.from({ length: idDesiredLength })
.map(() => {
return getRandomCharFromAlphabet(alphabet);
})
.join('');
}
export function wsJsonToRes(msg: WebSocketJsonResponse): WebSocketResponse {
let opStr: string = msg.op;
return {
op: UserOperation[opStr],
data: msg.data,
};
}
export const md = new markdown_it({
html: false,
linkify: true,
typographer: true,
})
.use(markdown_it_container, 'spoiler', {
validate: function (params: any) {
return params.trim().match(/^spoiler\s+(.*)$/);
},
render: function (tokens: any, idx: any) {
var m = tokens[idx].info.trim().match(/^spoiler\s+(.*)$/);
if (tokens[idx].nesting === 1) {
// opening tag
return `<details><summary> ${md.utils.escapeHtml(m[1])} </summary>\n`;
} else {
// closing tag
return '</details>\n';
}
},
})
.use(markdownitEmoji, {
defs: objectFlip(emojiShortName),
});
md.renderer.rules.emoji = function (token, idx) {
return twemoji.parse(token[idx].content);
};
export function hotRankComment(comment: Comment): number {
return hotRank(comment.score, comment.published);
}
export function hotRankPost(post: Post): number {
return hotRank(post.score, post.newest_activity_time);
}
export function hotRank(score: number, timeStr: string): number {
// Rank = ScaleFactor * sign(Score) * log(1 + abs(Score)) / (Time + 2)^Gravity
let date: Date = new Date(timeStr + 'Z'); // Add Z to convert from UTC date
let now: Date = new Date();
let hoursElapsed: number = (now.getTime() - date.getTime()) / 36e5;
let rank =
(10000 * Math.log10(Math.max(1, 3 + score))) /
Math.pow(hoursElapsed + 2, 1.8);
// console.log(`Comment: ${comment.content}\nRank: ${rank}\nScore: ${comment.score}\nHours: ${hoursElapsed}`);
return rank;
}
export function mdToHtml(text: string) {
return { __html: md.render(text) };
}
export function getUnixTime(text: string): number {
return text ? new Date(text).getTime() / 1000 : undefined;
}
export function addTypeInfo<T>(
arr: Array<T>,
name: string
): Array<{ type_: string; data: T }> {
return arr.map(e => {
return { type_: name, data: e };
});
}
export function canMod(
user: User,
modIds: Array<number>,
creator_id: number,
onSelf: boolean = false
): boolean {
// You can do moderator actions only on the mods added after you.
if (user) {
let yourIndex = modIds.findIndex(id => id == user.id);
if (yourIndex == -1) {
return false;
} else {
// onSelf +1 on mod actions not for yourself, IE ban, remove, etc
modIds = modIds.slice(0, yourIndex + (onSelf ? 0 : 1));
return !modIds.includes(creator_id);
}
} else {
return false;
}
}
export function isMod(modIds: Array<number>, creator_id: number): boolean {
return modIds.includes(creator_id);
}
const imageRegex = new RegExp(
/(http)?s?:?(\/\/[^"']*\.(?:jpg|jpeg|gif|png|svg|webp))/
);
const videoRegex = new RegExp(`(http)?s?:?(\/\/[^"']*\.(?:mp4))`);
export function isImage(url: string) {
return imageRegex.test(url);
}
export function isVideo(url: string) {
return videoRegex.test(url);
}
export function validURL(str: string) {
try {
return !!new URL(str);
} catch {
return false;
}
}
export function validEmail(email: string) {
let re = /^(([^\s"(),.:;<>@[\\\]]+(\.[^\s"(),.:;<>@[\\\]]+)*)|(".+"))@((\[(?:\d{1,3}\.){3}\d{1,3}])|(([\dA-Za-z\-]+\.)+[A-Za-z]{2,}))$/;
return re.test(String(email).toLowerCase());
}
export function capitalizeFirstLetter(str: string): string {
return str.charAt(0).toUpperCase() + str.slice(1);
}
export function routeSortTypeToEnum(sort: string): SortType {
if (sort == 'new') {
return SortType.New;
} else if (sort == 'hot') {
return SortType.Hot;
} else if (sort == 'topday') {
return SortType.TopDay;
} else if (sort == 'topweek') {
return SortType.TopWeek;
} else if (sort == 'topmonth') {
return SortType.TopMonth;
} else if (sort == 'topyear') {
return SortType.TopYear;
} else if (sort == 'topall') {
return SortType.TopAll;
}
}
export function routeListingTypeToEnum(type: string): ListingType {
return ListingType[capitalizeFirstLetter(type)];
}
export function routeDataTypeToEnum(type: string): DataType {
return DataType[capitalizeFirstLetter(type)];
}
export function routeSearchTypeToEnum(type: string): SearchType {
return SearchType[capitalizeFirstLetter(type)];
}
export async function getPageTitle(url: string) {
let res = await fetch(`/iframely/oembed?url=${url}`).then(res => res.json());
let title = await res.title;
return title;
}
export function debounce(
func: any,
wait: number = 1000,
immediate: boolean = false
) {
// 'private' variable for instance
// The returned function will be able to reference this due to closure.
// Each call to the returned function will share this common timer.
let timeout: any;
// Calling debounce returns a new anonymous function
return function () {
// reference the context and args for the setTimeout function
var context = this,
args = arguments;
// Should the function be called now? If immediate is true
// and not already in a timeout then the answer is: Yes
var callNow = immediate && !timeout;
// This is the basic debounce behaviour where you can call this
// function several times, but it will only execute once
// [before or after imposing a delay].
// Each time the returned function is called, the timer starts over.
clearTimeout(timeout);
// Set the new timeout
timeout = setTimeout(function () {
// Inside the timeout function, clear the timeout variable
// which will let the next execution run when in 'immediate' mode
timeout = null;
// Check if the function already ran with the immediate flag
if (!immediate) {
// Call the original function with apply
// apply lets you define the 'this' object as well as the arguments
// (both captured before setTimeout)
func.apply(context, args);
}
}, wait);
// Immediate mode and no wait timer? Execute the function..
if (callNow) func.apply(context, args);
};
}
export function getLanguage(): string {
let user = UserService.Instance.user;
let lang = user && user.lang ? user.lang : 'browser';
if (lang == 'browser') {
return getBrowserLanguage();
} else {
return lang;
}
}
export function getBrowserLanguage(): string {
return navigator.language;
}
export function getMomentLanguage(): string {
let lang = getLanguage();
if (lang.startsWith('zh')) {
lang = 'zh-cn';
} else if (lang.startsWith('sv')) {
lang = 'sv';
} else if (lang.startsWith('fr')) {
lang = 'fr';
} else if (lang.startsWith('de')) {
lang = 'de';
} else if (lang.startsWith('ru')) {
lang = 'ru';
} else if (lang.startsWith('es')) {
lang = 'es';
} else if (lang.startsWith('eo')) {
lang = 'eo';
} else if (lang.startsWith('nl')) {
lang = 'nl';
} else if (lang.startsWith('it')) {
lang = 'it';
} else if (lang.startsWith('fi')) {
lang = 'fi';
} else if (lang.startsWith('ca')) {
lang = 'ca';
} else if (lang.startsWith('fa')) {
lang = 'fa';
} else if (lang.startsWith('pl')) {
lang = 'pl';
} else if (lang.startsWith('pt')) {
lang = 'pt-br';
} else if (lang.startsWith('ja')) {
lang = 'ja';
} else if (lang.startsWith('ka')) {
lang = 'ka';
} else if (lang.startsWith('hi')) {
lang = 'hi';
} else if (lang.startsWith('el')) {
lang = 'el';
} else if (lang.startsWith('eu')) {
lang = 'eu';
} else if (lang.startsWith('gl')) {
lang = 'gl';
} else if (lang.startsWith('tr')) {
lang = 'tr';
} else if (lang.startsWith('hu')) {
lang = 'hu';
} else if (lang.startsWith('uk')) {
lang = 'uk';
} else {
lang = 'en';
}
return lang;
}
export function setTheme(theme: string = 'darkly', loggedIn: boolean = false) {
// unload all the other themes
for (var i = 0; i < themes.length; i++) {
let styleSheet = document.getElementById(themes[i]);
if (styleSheet) {
styleSheet.setAttribute('disabled', 'disabled');
}
}
// if the user is not logged in, we load the default themes and let the browser decide
if (!loggedIn) {
document.getElementById('default-light').removeAttribute('disabled');
document.getElementById('default-dark').removeAttribute('disabled');
} else {
document
.getElementById('default-light')
.setAttribute('disabled', 'disabled');
document
.getElementById('default-dark')
.setAttribute('disabled', 'disabled');
// Load the theme dynamically
let cssLoc = `/static/assets/css/themes/${theme}.min.css`;
loadCss(theme, cssLoc);
document.getElementById(theme).removeAttribute('disabled');
}
}
export function loadCss(id: string, loc: string) {
if (!document.getElementById(id)) {
var head = document.getElementsByTagName('head')[0];
var link = document.createElement('link');
link.id = id;
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = loc;
link.media = 'all';
head.appendChild(link);
}
}
export function objectFlip(obj: any) {
const ret = {};
Object.keys(obj).forEach(key => {
ret[obj[key]] = key;
});
return ret;
}
export function pictrsAvatarThumbnail(src: string): string {
// sample url: http://localhost:8535/pictrs/image/thumbnail256/gs7xuu.jpg
let split = src.split('/pictrs/image');
let out = `${split[0]}/pictrs/image/${
canUseWebP() ? 'webp/' : ''
}thumbnail96${split[1]}`;
return out;
}
export function showAvatars(): boolean {
return (
(UserService.Instance.user && UserService.Instance.user.show_avatars) ||
!UserService.Instance.user
);
}
// Converts to image thumbnail
export function pictrsImage(hash: string, thumbnail: boolean = false): string {
let root = `/pictrs/image`;
// Necessary for other servers / domains
if (hash.includes('pictrs')) {
let split = hash.split('/pictrs/image/');
root = `${split[0]}/pictrs/image`;
hash = split[1];
}
let out = `${root}/${canUseWebP() ? 'webp/' : ''}${
thumbnail ? 'thumbnail256/' : ''
}${hash}`;
return out;
}
export function isCommentType(item: Comment | PrivateMessage): item is Comment {
return (item as Comment).community_id !== undefined;
}
export function toast(text: string, background: string = 'success') {
let backgroundColor = `var(--${background})`;
Toastify({
text: text,
backgroundColor: backgroundColor,
gravity: 'bottom',
position: 'left',
}).showToast();
}
export function pictrsDeleteToast(
clickToDeleteText: string,
deletePictureText: string,
deleteUrl: string
) {
let backgroundColor = `var(--light)`;
let toast = Toastify({
text: clickToDeleteText,
backgroundColor: backgroundColor,
gravity: 'top',
position: 'right',
duration: 10000,
onClick: () => {
if (toast) {
window.location.replace(deleteUrl);
alert(deletePictureText);
toast.hideToast();
}
},
close: true,
}).showToast();
}
export function messageToastify(
creator: string,
avatar: string,
body: string,
link: string,
router: any
) {
let backgroundColor = `var(--light)`;
let toast = Toastify({
text: `${body}<br />${creator}`,
avatar: avatar,
backgroundColor: backgroundColor,
className: 'text-dark',
close: true,
gravity: 'top',
position: 'right',
duration: 5000,
onClick: () => {
if (toast) {
toast.hideToast();
router.history.push(link);
}
},
}).showToast();
}
export function setupTribute(): Tribute {
return new Tribute({
collection: [
// Emojis
{
trigger: ':',
menuItemTemplate: (item: any) => {
let shortName = `:${item.original.key}:`;
let twemojiIcon = twemoji.parse(item.original.val);
return `${twemojiIcon} ${shortName}`;
},
selectTemplate: (item: any) => {
return `:${item.original.key}:`;
},
values: Object.entries(emojiShortName).map(e => {
return { key: e[1], val: e[0] };
}),
allowSpaces: false,
autocompleteMode: true,
menuItemLimit: mentionDropdownFetchLimit,
menuShowMinLength: 2,
},
// Users
{
trigger: '@',
selectTemplate: (item: any) => {
return `[/u/${item.original.key}](/u/${item.original.key})`;
},
values: (text: string, cb: any) => {
userSearch(text, (users: any) => cb(users));
},
allowSpaces: false,
autocompleteMode: true,
menuItemLimit: mentionDropdownFetchLimit,
menuShowMinLength: 2,
},
// Communities
{
trigger: '#',
selectTemplate: (item: any) => {
return `[/c/${item.original.key}](/c/${item.original.key})`;
},
values: (text: string, cb: any) => {
communitySearch(text, (communities: any) => cb(communities));
},
allowSpaces: false,
autocompleteMode: true,
menuItemLimit: mentionDropdownFetchLimit,
menuShowMinLength: 2,
},
],
});
}
let tippyInstance = tippy('[data-tippy-content]');
export function setupTippy() {
tippyInstance.forEach(e => e.destroy());
tippyInstance = tippy('[data-tippy-content]', {
delay: [500, 0],
// Display on "long press"
touch: ['hold', 500],
});
}
function userSearch(text: string, cb: any) {
if (text) {
let form: SearchForm = {
q: text,
type_: SearchType[SearchType.Users],
sort: SortType[SortType.TopAll],
page: 1,
limit: mentionDropdownFetchLimit,
};
WebSocketService.Instance.search(form);
this.userSub = WebSocketService.Instance.subject.subscribe(
msg => {
let res = wsJsonToRes(msg);
if (res.op == UserOperation.Search) {
let data = res.data as SearchResponse;
let users = data.users.map(u => {
return { key: u.name };
});
cb(users);
this.userSub.unsubscribe();
}
},
err => console.error(err),
() => console.log('complete')
);
} else {
cb([]);
}
}
function communitySearch(text: string, cb: any) {
if (text) {
let form: SearchForm = {
q: text,
type_: SearchType[SearchType.Communities],
sort: SortType[SortType.TopAll],
page: 1,
limit: mentionDropdownFetchLimit,
};
WebSocketService.Instance.search(form);
this.communitySub = WebSocketService.Instance.subject.subscribe(
msg => {
let res = wsJsonToRes(msg);
if (res.op == UserOperation.Search) {
let data = res.data as SearchResponse;
let communities = data.communities.map(u => {
return { key: u.name };
});
cb(communities);
this.communitySub.unsubscribe();
}
},
err => console.error(err),
() => console.log('complete')
);
} else {
cb([]);
}
}
export function getListingTypeFromProps(props: any): ListingType {
return props.match.params.listing_type
? routeListingTypeToEnum(props.match.params.listing_type)
: UserService.Instance.user
? UserService.Instance.user.default_listing_type
: ListingType.All;
}
// TODO might need to add a user setting for this too
export function getDataTypeFromProps(props: any): DataType {
return props.match.params.data_type
? routeDataTypeToEnum(props.match.params.data_type)
: DataType.Post;
}
export function getSortTypeFromProps(props: any): SortType {
return props.match.params.sort
? routeSortTypeToEnum(props.match.params.sort)
: UserService.Instance.user
? UserService.Instance.user.default_sort_type
: SortType.Hot;
}
export function getPageFromProps(props: any): number {
return props.match.params.page ? Number(props.match.params.page) : 1;
}
export function editCommentRes(
data: CommentResponse,
comments: Array<Comment>
) {
let found = comments.find(c => c.id == data.comment.id);
if (found) {
found.content = data.comment.content;
found.updated = data.comment.updated;
found.removed = data.comment.removed;
found.deleted = data.comment.deleted;
found.upvotes = data.comment.upvotes;
found.downvotes = data.comment.downvotes;
found.score = data.comment.score;
}
}
export function saveCommentRes(
data: CommentResponse,
comments: Array<Comment>
) {
let found = comments.find(c => c.id == data.comment.id);
if (found) {
found.saved = data.comment.saved;
}
}
export function createCommentLikeRes(
data: CommentResponse,
comments: Array<Comment>
) {
let found: Comment = comments.find(c => c.id === data.comment.id);
if (found) {
found.score = data.comment.score;
found.upvotes = data.comment.upvotes;
found.downvotes = data.comment.downvotes;
if (data.comment.my_vote !== null) {
found.my_vote = data.comment.my_vote;
}
}
}
export function createPostLikeFindRes(data: PostResponse, posts: Array<Post>) {
let found = posts.find(c => c.id == data.post.id);
if (found) {
createPostLikeRes(data, found);
}
}
export function createPostLikeRes(data: PostResponse, post: Post) {
if (post) {
post.score = data.post.score;
post.upvotes = data.post.upvotes;
post.downvotes = data.post.downvotes;
if (data.post.my_vote !== null) {
post.my_vote = data.post.my_vote;
}
}
}
export function editPostFindRes(data: PostResponse, posts: Array<Post>) {
let found = posts.find(c => c.id == data.post.id);
if (found) {
editPostRes(data, found);
}
}
export function editPostRes(data: PostResponse, post: Post) {
if (post) {
post.url = data.post.url;
post.name = data.post.name;
post.nsfw = data.post.nsfw;
}
}
export function commentsToFlatNodes(
comments: Array<Comment>
): Array<CommentNodeI> {
let nodes: Array<CommentNodeI> = [];
for (let comment of comments) {
nodes.push({ comment: comment });
}
return nodes;
}
export function commentSort(tree: Array<CommentNodeI>, sort: CommentSortType) {
// First, put removed and deleted comments at the bottom, then do your other sorts
if (sort == CommentSortType.Top) {
tree.sort(
(a, b) =>
+a.comment.removed - +b.comment.removed ||
+a.comment.deleted - +b.comment.deleted ||
b.comment.score - a.comment.score
);
} else if (sort == CommentSortType.New) {
tree.sort(
(a, b) =>
+a.comment.removed - +b.comment.removed ||
+a.comment.deleted - +b.comment.deleted ||
b.comment.published.localeCompare(a.comment.published)
);
} else if (sort == CommentSortType.Old) {
tree.sort(
(a, b) =>
+a.comment.removed - +b.comment.removed ||
+a.comment.deleted - +b.comment.deleted ||
a.comment.published.localeCompare(b.comment.published)
);
} else if (sort == CommentSortType.Hot) {
tree.sort(
(a, b) =>
+a.comment.removed - +b.comment.removed ||
+a.comment.deleted - +b.comment.deleted ||
hotRankComment(b.comment) - hotRankComment(a.comment)
);
}
// Go through the children recursively
for (let node of tree) {
if (node.children) {
commentSort(node.children, sort);
}
}
}
export function commentSortSortType(tree: Array<CommentNodeI>, sort: SortType) {
commentSort(tree, convertCommentSortType(sort));
}
function convertCommentSortType(sort: SortType): CommentSortType {
if (
sort == SortType.TopAll ||
sort == SortType.TopDay ||
sort == SortType.TopWeek ||
sort == SortType.TopMonth ||
sort == SortType.TopYear
) {
return CommentSortType.Top;
} else if (sort == SortType.New) {
return CommentSortType.New;
} else if (sort == SortType.Hot) {
return CommentSortType.Hot;
} else {
return CommentSortType.Hot;
}
}
export function postSort(
posts: Array<Post>,
sort: SortType,
communityType: boolean
) {
// First, put removed and deleted comments at the bottom, then do your other sorts
if (
sort == SortType.TopAll ||
sort == SortType.TopDay ||
sort == SortType.TopWeek ||
sort == SortType.TopMonth ||
sort == SortType.TopYear
) {
posts.sort(
(a, b) =>
+a.removed - +b.removed ||
+a.deleted - +b.deleted ||
(communityType && +b.stickied - +a.stickied) ||
b.score - a.score
);
} else if (sort == SortType.New) {
posts.sort(
(a, b) =>
+a.removed - +b.removed ||
+a.deleted - +b.deleted ||
(communityType && +b.stickied - +a.stickied) ||
b.published.localeCompare(a.published)
);
} else if (sort == SortType.Hot) {
posts.sort(
(a, b) =>
+a.removed - +b.removed ||
+a.deleted - +b.deleted ||
(communityType && +b.stickied - +a.stickied) ||
hotRankPost(b) - hotRankPost(a)
);
}
}
export const colorList: Array<string> = [
hsl(0),
hsl(100),
hsl(150),
hsl(200),
hsl(250),
hsl(300),
];
function hsl(num: number) {
return `hsla(${num}, 35%, 50%, 1)`;
}
function randomHsl() {
return `hsla(${Math.random() * 360}, 100%, 50%, 1)`;
}
export function previewLines(text: string, lines: number = 3): string {
// Use lines * 2 because markdown requires 2 lines
return text
.split('\n')
.slice(0, lines * 2)
.join('\n');
}
function canUseWebP() {
// TODO pictshare might have a webp conversion bug, try disabling this
return false;
// var elem = document.createElement('canvas');
// if (!!(elem.getContext && elem.getContext('2d'))) {
// var testString = !(window.mozInnerScreenX == null) ? 'png' : 'webp';
// // was able or not to get WebP representation
// return (
// elem.toDataURL('image/webp').startsWith('data:image/' + testString)
// );
// }
// // very old browser like IE 8, canvas not supported
// return false;
}