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

Simply put, +_ is equivalent to using the Number() constructor.

In fact, it even works on dates:

var d = new Date('03/27/2014');
console.log(Number(d)) // returns 1395903600000
console.log(+d) // returns 1395903600000

DEMO: http://jsfiddle.net/dirtyd77/GCLjd/

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More information can also be found on MDN - Unary plus (+) section:

The unary plus operator precedes its operand and evaluates to its operand but attempts to converts it into a number, if it isn't already. Although unary negation (-) also can convert non-numbers, unary plus is the fastest and preferred way of converting something into a number, because it does not perform any other operations on the number. It can convert string representations of integers and floats, as well as the non-string values true, false, and null. Integers in both decimal and hexadecimal ("0x"-prefixed) formats are supported. Negative numbers are supported (though not for hex). If it cannot parse a particular value, it will evaluate to NaN.