New Jersey Statutes Title 2A. Administration of Civil and Criminal Justice 2A § 34-70

a. Except as otherwise provided in section 16 of this act,  1 a court of this State may not exercise its jurisdiction under this article if at the time of the commencement of the proceeding a proceeding concerning the custody of the child had been commenced in a court of another state having jurisdiction substantially in conformity with this act, unless the proceeding has been terminated or is stayed by the court of the other state because a court of this State is a more convenient forum under section 19 of this act.  2

b. Except as otherwise provided in section 16 of this act, a court of this State, before hearing a child custody proceeding, shall examine the court documents and other information supplied by the parties pursuant to section 21 of this act.  3 If the court determines that a child custody proceeding was previously commenced in a court in another state having jurisdiction substantially in accordance with this act, the court of this State shall stay its proceeding and communicate with the court of the other state. If the court of the state having jurisdiction substantially in accordance with this act does not determine that the court of this State is a more appropriate forum, the court of this State shall dismiss the proceeding.

c. In a proceeding to modify a child custody determination, a court of this State shall determine whether a proceeding to enforce the determination has been commenced in another state. If a proceeding to enforce a child custody determination has been commenced in another state, the court may: