Update Entity from JavaScript in Ms Dynamics CRM 2011/2013 using OData endpoint

Posting this for future reference:

function updateEntity(entityName, id, entity ) {

    var url = oDataUrl + "/" + entityName + "Set(guid'" + id + "')";

    entityData = window.JSON.stringify(entity);

    return $.ajax({
        type: "POST",
        contentType: "application/json;charset=utf-8",
        datatype: "json",
        data: entityData,
        url: url,
        beforeSend: function (x) {
            x.setRequestHeader("Accept", "application/json");
            x.setRequestHeader("X-HTTP-Method", "MERGE")
        },
    });
}

entityName is the logical entity name.
id is the Id of the record that we want to update
entity is a object that contains that values that need changing.
 e.g.:

 account = {};
 account.Name = "New Name"; 

 oDataUrl is the Url of the OData endpoint for your organization