{} + [] - why it is 0 or [object Object]?

Question

If you open a JS Console in your browser (in my case Chrome) and type:

{} + []

you will get 0, but when you type

console.lo         


        

Answer 1

When you see {} character at the beginning it is interpreted as a empty block or empty object literal(when you're creating objects).

When you're using an expression or statement, + represent the plus operator, which coerces its operand(in this case it will be []) to a number.

So +[] is the same as Number([]), which evaluates to 0.

The unary plus operator internally use the ToNumber abstract operation.

Read more about Type Conversions and operators.

console.log(Number([]));

With the other words, {} + [] expression is an empty code block followed by an array which will be constraint to a number(Number[]).

In the second example you're providing you just concat an object literal(empty object) to an array. That't why you're receiving [object Object].