Check is Streak installed

isStreakInstalled.js

var INSTALL_CHECK = 'chrome-extension://pnnfemgpilpdaojpnkjdgfgbnnjojfik/blank.png';

function isExtensionInstalled() {
	//we have different logic for Chrome vs Safari
	if(BrowserDetect.browser === 'Chrome'){
		// the Chrome extension makes an image "web accessible", so we have the page try to load that image.
		// if it loads successfully then the Streak extension is installed. If the image does not load successfully, then the image is not installed
		var img = new Image();
		img.onload = function() {
			clearInterval(installTimerId);
			streakIsInstalled();
		};
		img.onerror = function(){
		};
		try {
			img.src = INSTALL_CHECK;
		}
		catch (error) {
		}
	}
	else{
		// for Safari, we have our Safari extension add an element to the page with id "streakExists" when going to a 
		// streak page. So we have our script look for that element. If we can find it then we're good
		if( document.getElementById('streakExists')){
			clearInterval(installTimerId);
			streakIsInstalled();
		}
	}
}

// we poll because sometimes it takes time for the marker element to get added
function intervalCheckInstalled(max){
	var current = 0;
	var delay = 500;
	installTimerId = setInterval(function(){
		current += delay;
		if(current > max){
			clearInterval(installTimerId);
			streakIsNotInstalled();
		}
		isExtensionInstalled();
	}, delay);
	isExtensionInstalled();
}

// our current homepage checks for 2 seconds
intervalCheckInstalled(2000);