_.size

Returns the number of values in the collection.

// Underscore/Lodash
var result = _.size({one: 1, two: 2, three: 3})
console.log(result)
// output: 3
 
// Native
var result2 = Object.keys({one: 1, two: 2, three: 3}).length
console.log(result2)
// output: 3

Browser Support for Object.keys()

5.0 ✔	✔	4.0 ✔	9.0 ✔	12.0 ✔	5.0 ✔