JS in the + number cast small example

1 <script>2         console.log (([]+{}). length); 3     </script>4 
The output is actually:
Why would it be 15?
Because the + sign is coerced into a string under {}, the object is actually "{object}" plus two spaces in the middle of the object and "["
"]" These two curly braces are 12 letters of two object, so there are 15 characters appearing.
Let's switch to the following code output:
1  <script>2         console.log (([]+{}). length); 3         Console.log ([]+{}); 4     </script>
JS in the + number cast small example