I thought that got dropped from &quot;HTML5&quot; and was considered deprecated?<p>It was never implemented directly in IE or Edge (<a href="http:&#x2F;&#x2F;caniuse.com&#x2F;#feat=eventsource" rel="nofollow">http:&#x2F;&#x2F;caniuse.com&#x2F;#feat=eventsource</a>), so when you say &quot;work in all browsers&quot; do you discount IE or can you recommend a good well-supported polyfill?