therajumandapati · June 10, 2015 13:58 · butchpeters · Jun 10, 2015
diff --git a/coercion.js b/coercion.js
 +[] evaluates to the number zero, because unary-plus tries to convert any value to a number, so that leaves
 
 ++[[]][0]+[0]
 
 [[]][0] is an expression accessing the first element in the array, which is a reference to the inner array. This is shorthand for x = [[]]; x[0];, if it helps you see it better.
 
 ++[[]][0] then evaluates to a pre-increment of the first element in the array, which returns the value after the element is incremented.  Because an array is not numeric, it first needs to coerce it to a number.  We saw before that an empty array coerces to 0, so incrementing 0 is 1.  If we had a reference to [[]], we’d see that it becomes [1] after the increment operation. (i.e. x = [[]]; ++x[0] // returns 1, and x is now [1])
 
 So, this whole expression boils down to 1 + [0].  Since a number and an array can’t normally be added together, javascript converts both values to strings and concatenates them.
 
 1.toString() + [0].toString()
 
 “1” + “0”
 
 “10”
	+[] evaluates to the number zero, because unary-plus tries to convert any value to a number, so that leaves

	++[[]][0]+[0]

	[[]][0] is an expression accessing the first element in the array, which is a reference to the inner array. This is shorthand for x = [[]]; x[0];, if it helps you see it better.

	++[[]][0] then evaluates to a pre-increment of the first element in the array, which returns the value after the element is incremented. Because an array is not numeric, it first needs to coerce it to a number. We saw before that an empty array coerces to 0, so incrementing 0 is 1. If we had a reference to [[]], we’d see that it becomes [1] after the increment operation. (i.e. x = [[]]; ++x[0] // returns 1, and x is now [1])

	So, this whole expression boils down to 1 + [0]. Since a number and an array can’t normally be added together, javascript converts both values to strings and concatenates them.

	1.toString() + [0].toString()

	“1” + “0”

	“10”