Why does {} - 1 give -1 result in browser javascript?
As per my understanding of how type coercion works here, first valueOf() will be called on the {}, which is not a primitive value, so next toString() will be called, which gives [object Object]. That would give us '[object Object]' - 1, so NaN, however it actually results in -1.
In node this seems to work as per my understanding, as the result is NaN there.
In the console, for involved reasons, {} - 1 is evaluated as if you had typed
{
// no statements
}
-1;
It's a block statement followed by the expression -1.
If you type ({} - 1) to force evaluation as an expression, you get NaN.
The console REPL is not simply an expression evaluator; it attempts to evaluate and run anything you type as a sequence of statements. A statement that starts with { is always disambiguated as being the start of a block of statements, never as an object initializer.