Neither underscore nor lodash use a for loop. Both use the native Object.keys when available. underscore uses native Array#forEach and lodash uses a while loop.

Neither underscore nor lodash use a for loop. Both use the native Object.keys when available. underscore uses native Array#forEach and lodash uses a while loop. So only lodash forEach is actually faster. lodash is the only one to be performance focused. underscore always uses the native methods when possible.