NJ has adopted the Uniform Probate Code Section 2-701 which allows for spouses to contract to make a will.
This is especially helpful in situations where there may be some concern that the surviving spouse might change his or her Last Will and Testament after the death of the first spouse. This is typically seen in second marriage situations where both spouses have children from previous marriages. In those cases, if the spouses had initially agreed to create reciprocal Wills leaving everything to each other (surviving spouse) but after the second death, the assets would pass to their respective children, it is very possible that the wishes may never be fulfilled. The surviving spouse could change the Will after the first death and leave everything to his or her own children instead. There is no guarantee that the surviving spouse will honor the decedent’s wishes and follow through with the initial testamentary dispositions. The surviving spouse could change the Will to eliminate the children of the surviving spouse.
A way around this problem is to have the couples execute a contract that provides that each spouse agrees not to change or revoke the Will after the death of the first spouse. This binding contract will be upheld in a court of law and at a minimum, offer evidentiary proof as to the initial motives of the testators.
 Summarized from Representing the Elderly Client, by Thomas Begley and Jo-Anne Herina Jeffreys