SP.FieldLookup.isRelationship property (sp.js)
Gets or sets a value that specifies whether this lookup field is returned by SP.List.getRelatedFields from the list being looked up to.
Applies to: apps for SharePoint | SharePoint Foundation 2013 | SharePoint Server 2013
var value = SP.FieldLookup.get_isRelationship ()
var value = SP.FieldLookup.set_isRelationship ()
true if the field is discoverable from the list to which it looks for its value; otherwise, false.
A lookup field is discoverable from the list to which it looks for its value when the source list's SP.List.getRelatedFields method returns a collection that contains an SP.RelatedField object with information about the lookup field.
The IsRelationship property returns false if the SP.FieldLookup object represents a secondary column in a multiple column lookup. Secondary columns are not discoverable from the source list.