Ext JS 4 Proxy that puts params in JSON format, that can be used by Stores.

Ext.ux.data.proxy.JsonAjaxProxy.js

Ext.define('Ext.ux.data.proxy.JsonAjaxProxy', {
	extend:'Ext.data.proxy.Ajax',
	alias:'proxy.jsonajax',

	actionMethods : {
		create: "POST",
		read: "POST",
		update: "POST",
		destroy: "POST"
	},

	buildRequest:function (operation) {
		var request = this.callParent(arguments);

	        // For documentation on jsonData see Ext.Ajax.request
        	request.jsonData = request.params;
        	request.params = {};

	        return request;
	},

	/*
	 * @override
	 * Inherit docs. We don't apply any encoding here because
	 * all of the direct requests go out as jsonData
	 */
	applyEncoding: function(value){
		return value;
	}

});

Good to know, thanks!