Working of crypto currency swaping (Exchanging) in Crypto exchange I am new in crypto. I know something about cryto currency and its working. I am curiosity about the working of Crypto exchange like binance,coinbase...etc... My doubts is 


Some exchanges provide the swapping facilities like one click swapping from one cryto currency to another(That is without use of trading mechanism of buy order and sell order)...How it is possible ? 
Actually the exchanges is hold a large amount of crypto asset for the users to provide one click swapping facilities to the users ....???


I expect a detailed explanation as possible from this community. Thanks
Any service or exchange allowing conversion of one asset into another (whether it is decentralized or centralized), is eventually executing the trade on an orderbook with a large exchange or liquidity provider.

Larger exchanges like Coinbase, Binance, Bitstamp etc. operate their own orderbooks, which have liquidity from users and market makers.

Second tier services like Shapeshift, Changelly etc. maintain balances in all the coins they support on larger services, and when a user wishes to convert an asset, they will execute a corresponding trade on these services.