NEW YORK — Best Buy’s profit jumped 21 percent as the nation’s largest consumer electronics retailer increased sales online and tried to create a better shopping experience in the stores while it also cut costs.

Its shares soared 19 percent after the company said online sales rose 24 percent to $835 million, a beacon for investors who have watched Amazon.com eat away at the sales of almost every traditional retailer. The stock surge marked the largest daily percentage increase since mid-December 2008.

Revenue at established stores, an important measure of a retailer’s health, also managed a gain of 0.8 percent when Wall Street, according to a survey by FactSet, had expected a decline of 0.4 percent. The company has been working on revamping its stores and improving sales staff training to convert browsers into buyers.