Why does `{} + []` return a different result from `a = {} + []` in Javascript?

Question

In (at least) Firefox Web Console and JSBin, I get

> {} + []
0
> a = {} + []
\"[object Object]\"

Node.js returns \"[object Obje

Answer 1

On the browser console, when it isn't preceded by a = (or some other code that changes its context), {} is treated as a block, not an object literal.

Since the block is empty it does nothing, leaving + [].

The unary plus operator converts the array to a number, which is 0.