The US constitution allowed for certain laws to be amended over time and the Bill of Rights gave US citizens certain rights which could never be taken away from them, if they are, they can overthrow the government.
The 1979 revolution was a popular revolution against an autocratic but progressive monarch which turned into a backwards religious movement sending Iran back 200 years in time.
The Arab spring was a popular revolution sparked by demands for democracy against horrible dictators, which ultimately backfired due to civil war following the coups in Yemen, Syria and Libya, unrest in Egypt due to political tensions and high unemployment in Tunisia.
Differences:
Iranian Revolution eventually grew into religious movement, Arab spring was a pro-democracy movement
Arab spring results in civil war, unrest and bad economic times, Iranian Revolution results in Invasion form Iraq and oppression by the government.
