bypassing chrome intl timezone bug fix #517

moment-timezone.js

@@ -330,7 +330,7 @@
 		// use Intl API when available and returning valid time zone
 		try {
 			var intlName = Intl.DateTimeFormat().resolvedOptions().timeZone;
-			if (intlName){
+			if (isIntlNameCredible(intlName)){
 				var name = names[normalizeName(intlName)];
 				if (name) {
 					return name;
@@ -360,6 +360,27 @@
 		return zoneScores.length > 0 ? zoneScores[0].zone.name : undefined;
 	}
 
+	// for issue: https://github.com/moment/moment-timezone/issues/517
+	function isIntlNameCredible (intlName) {
+		if (!intlName) {
+			return false;
+		}
+
+		var zone = getZone(intlName),
+			browserOffset = new Date().getTimezoneOffset(),
+			i,
+			validOffset;
+		if (zone) {
+			for (i = 0; i < zone.offsets.length && !validOffset; i++) {
+				if (zone.offsets[i].offset === browserOffset) {
+					validOffset = zone.offsets[i].offset;
+				}
+			}
+		}
+
+		return !!validOffset;
+	}
+
 	function guess (ignoreCache) {
 		if (!cachedGuess || ignoreCache) {
 			cachedGuess = rebuildGuess();

tests/moment-timezone/guess.js

@@ -77,9 +77,11 @@ exports.guess = {
 
 	"When Intl is available, it is used" : function (test) {
 		mockIntlTimeZone('Europe/London');
+		mockTimezoneOffset(tz.zone('Europe/London'));
 		test.equal(tz.guess(true), 'Europe/London');
 
 		mockIntlTimeZone('America/New_York');
+		mockTimezoneOffset(tz.zone('America/New_York'));
 		test.equal(tz.guess(true), 'America/New_York');
 
 		mockIntlTimeZone('America/Some_Missing_Zone');
@@ -95,7 +97,7 @@ exports.guess = {
 		console.error = function (message) {
 			errors += message;
 		};
-		
+
 		mockIntlTimeZone(undefined);
 		mockTimezoneOffset(tz.zone('Europe/London'));
 		test.equal(tz.guess(true), 'Europe/London');
@@ -115,5 +117,17 @@ exports.guess = {
 			test.ok(tz.guess(true), "Should have a guess for " + zone.name + ")");
 		}
 		test.done();
+	},
+
+	"check Intl.DateTimeFormat().resolvedOptions().timeZone is credible" : function (test) {
+		mockTimezoneOffset(tz.zone('Asia/Shanghai'));
+		mockIntlTimeZone('America/Chicago');
+		var guessedName = tz.guess(true);
+		test.equal(
+			tz.zone(guessedName).offset(Date.now()),
+			tz.zone('Asia/Shanghai').offset(Date.now()),
+			"Should have a guess like Asia/Shanghai)",
+		);
+		test.done();
 	}
 };