The above answer is incorrect.  Effective 2018 like-kind exchanges of personal property no longer qualify, therefore the concept of trade-in deferral no longer exists (horrible on vehicles) therefore it is treated as a sale of the old and purchase of the new.  See below.

IR-2018-227, November 19, 2018

WASHINGTON — The Internal Revenue Service today reminded taxpayers that like-kind exchange tax treatment is now generally limited to exchanges of real property. The Tax Cuts and Jobs Act, passed in December 2017, made tax law changes that will affect virtually every business and individual in 2018 and the years ahead. 

Effective Jan. 1, 2018, exchanges of personal or intangible property such as machinery, equipment, vehicles, artwork, collectibles, patents, and other intellectual property generally do not qualify for nonrecognition of gain or loss as like-kind exchanges. However, certain exchanges of mutual ditch, reservoir or irrigation stock are still eligible.

Like-kind exchange treatment now applies only to exchanges of real property that is held for use in a trade or business or for investment. Real property, also called real estate, includes land and generally anything built on or attached to it. An exchange of real property held primarily for sale still does not qualify as a like-kind exchange.

A transition rule in the new law allows like-kind treatment for some exchanges of personal or intangible property. If the taxpayer disposed of the personal or intangible property on or before Dec. 31, 2017, or received replacement property on or before that date, the exchange may qualify for like-kind exchange treatment.