https://brandanalytics.ru/app/ba_front/js/vendor/fontloader.js

1//This script must be placed in the HEAD above all external stylesheet declarations (link[rel=stylesheet])
2function loadFont(fontName, woffUrl, woff2Url, onlyLoadFontOnSecondPageload) {
3  // 1. Setting up localStorage
4  const loSto = localStorage || {},
5    localStoragePrefix = 'x-font-' + fontName,
6    localStorageUrlKey = localStoragePrefix + 'url',
7    localStorageCssKey = localStoragePrefix + 'css',
8    storedFontUrl = loSto[localStorageUrlKey],
9    storedFontCss = loSto[localStorageCssKey];
10  
11  // 2. Setting up the <style> element, that we are using to apply the base64 encoded font data
12  let styleElement = document.createElement('style');
13  styleElement.rel = 'stylesheet';
14  document.head.appendChild(styleElement);
15  // Setting styleElement.textContent must be after this line, because of IE9 errors
16  
17  // 3. Checking whether the font data is already in localStorage and up-to-date
18  if (storedFontCss && (storedFontUrl === woffUrl || storedFontUrl === woff2Url)) {
19    // the css is still in the localStorage
20        // AND it was loaded from one of the current URLs
21
22        // 4. Applying the font style sheet
23        styleElement.textContent = storedFontCss;
24
25    } else {
26        // The data was not present, or loaded from an obsolete URL
27        // So we have to load it again
28
29        // 5. Checking for WOFF2 support to know which URL we should use
30    const url = (woff2Url)
31      ? woff2Url // WOFF2 URL provided and supported
32      : woffUrl; // only WOFF support
33
34        // 6. Fetching the font data from the server
35    const request = new XMLHttpRequest();
36        request.open('GET', url);
37        request.onload = function() {
38            if (request.status >= 200 && request.status < 400) {
39                // 7. Updating localStorage with the fresh data and applying the font data
40                loSto[localStorageUrlKey] = url;
41                loSto[localStorageCssKey] = request.responseText;
42                if (!onlyLoadFontOnSecondPageload) {
43                    styleElement.textContent = request.responseText;
44                }
45            }
46        };
47        request.send();
48    }
49}