Detect JSON Ajax requests by the response content-type (like is done with XML). Fixes #5709.

src/ajax.js

@@ -557,6 +557,7 @@ jQuery.extend({
 	httpData: function( xhr, type, s ) {
 		var ct = xhr.getResponseHeader("content-type"),
 			xml = type === "xml" || !type && ct && ct.indexOf("xml") >= 0,
+			json = type === "json" || !type && ct && ct.indexOf("json") >= 0,
 			data = xml ? xhr.responseXML : xhr.responseText;
 
 		if ( xml && data.documentElement.nodeName === "parsererror" ) {
@@ -578,7 +579,7 @@ jQuery.extend({
 			}
 
 			// Get the JavaScript object, if JSON is used.
-			if ( type === "json" ) {
+			if ( json ) {
 				// Try to use the native JSON parser first
 				try {
 					data = JSON.parse( data );

test/data/json.php

@@ -1,9 +1,13 @@
 <?php
 error_reporting(0);
+if ( $_REQUEST['header'] ) {
+	header("Content-type: application/json");
+}
+
 $json = $_REQUEST['json'];
 if($json) {
 	echo '[ {"name": "John", "age": 21}, {"name": "Peter", "age": 25 } ]';
 } else {
 	echo '{ "data": {"lang": "en", "length": 25} }';
 }
-?>
+?>

test/unit/ajax.js

@@ -797,6 +797,25 @@ test("jQuery.ajax() - script, Remote with scheme-less URL", function() {
 	});
 });
 
+test("jQuery.ajax() - json by content-type", function() {
+	expect(5);
+
+	stop();
+
+	jQuery.ajax({
+		url: "data/json.php",
+		data: { header: "json", json: "array" },
+		success: function( json ) {
+	  		ok( json.length >= 2, "Check length");
+	  		equals( json[0].name, 'John', 'Check JSON: first, name' );
+	  		equals( json[0].age, 21, 'Check JSON: first, age' );
+	  		equals( json[1].name, 'Peter', 'Check JSON: second, name' );
+	  		equals( json[1].age, 25, 'Check JSON: second, age' );
+	  		start();
+		}
+	});
+});
+
 test("jQuery.getJSON(String, Hash, Function) - JSON array", function() {
 	expect(5);
 	stop();