Font Face Observer is a small @font-face loader and monitor (3.5KB minified and 1.3KB gzipped) compatible with any webfont service. It will monitor when a webfont is loaded and notify you. It does not limit you in any way in where, when, or how you load your webfonts. Unlike the Web Font Loader Font Face Observer uses scroll events to detect font loads efficiently and with minimum overhead. The FontFaceObserver constructor takes two arguments: the font-family name (required) and an object describing the variation (optional). The object can contain weight, style, and stretch properties. If a property is not present it will default to normal. To start loading the font, call the load method. It'll immediately return a new Promise that resolves when the font is loaded and rejected when the font fails to load.