What does = +_ mean in JavaScript

Question

I was wondering what the = +_ operator means in JavaScript. It looks like it does assignments.

Example:

hexbin.radius = function(_)         


        

Answer 1

_ is just a a variable name, passed as a parameter of function hexbin.radius , and + cast it into number

Let me make a exmple same like your function .

var hexbin = {},r  ;

hexbin.radius = function(_) {
   if (!arguments.length)
      return r;
   console.log( _ , typeof _ )    
   r = +_;
   console.log( r , typeof r , isNaN(r) );   
}

and run this example function .. which outputs

hexbin.radius( "1");

1 string
1 number false 

hexbin.radius( 1 );

1 number
1 number false

hexbin.radius( [] );

[] object
0 number false

hexbin.radius( 'a' );

a string
NaN number true

hexbin.radius( {} );

Object {} object
NaN number true

hexbin.radius( true );

true boolean
1 number false