Hieroglyphics is a written language, where words and letters are represented by images. Although no longer in use today, there are also many languages which are also extinct; this does not invalidate them as languages. At one point in time, they were essential.
Emojis are the first means of universal communication. While historically symbols as language may have been employed, emojis are the first "universal language". Most emojis are able to be understood by anyone, regardless of culture, language, or background. Hieroglyphs, however, are known only to their respective cultures, requiring historians and translators to attempt to glean meaning. In this way, emojis have many parallels to hieroglyphs, but are ultimately revolutionary due to their accessibility. As more and more people use emojis in place of words or even entire thoughts, it is becoming an essential part of our daily written language.