I need help understanding the code below. It's a bit confusing to me, but I really want to understand it.
reverse = [-1, 1][+!!reverse];
I need help understanding the code below. It's a bit confusing to me, but I really want to understand it.
reverse = [-1, 1][+!!reverse];
Assume the value of reverse is 5. When we evaluate !5, it becomes false because all numbers except 0 are considered truthy. If we negate false one more time, we get true. Finally, we can convert this boolean expression to either 1 or 0 by using the + operator.
var reverse = 5;
reverse = [-1, 1][+!!reverse];
This is effectively the same as:
var reverse = 5;
reverse = [-1, 1][1];
To clarify further, the expression could also be written as:
var reverse = 5;
reverse = [-1, 1][Number(Boolean(reverse))];
Here we have a piece of code crafted by someone who fancied themselves clever, overlooking the importance of not just speed but also readability in great code.
The opening segment
[-1,1]
creates an array with -1 at index 0 and 1 at index 1.
!!reverse
Changes the value of reverse to a boolean true.
When the unary + operator (operators that take only one argument) is applied, it converts the boolean value of reverse into a number.
Effectively, this means that if reverse is true, it becomes 1. If reverse is false, it becomes -1.
!!reverse will change the variables to a boolean value
+!!reverse' will convert it to either 0 or 1
The resulting number is then used as an index for the array on the left side
Therefore, this entire expression will assign reverse to -1 if the original value was false, or 1 if it was true
A more concise way to express the above would be
reverse = reverse? 1:-1;
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