Single plus operator in javascript [duplicate]

Question

Just saw this in underscore's source:

if (obj.length === +obj.length) {     ... } 

What does the plus do? I never saw this before.

Is it considered a good practice among developers?

Answer 1

The plus converts a string to a float. The code you provided is equivalent to the following:

if ( obj.length === Number(obj.length) ) {     // ... }