What is the reason behind
++[[]][0] == 1
While trying to do
++[]
leads to an error?
Shouldn't they produce the same result? My understanding is that the first example performs an index-read on the array, resulting in an array within an array. Then the increment operation is carried out. If this is the case, why does the second example not work?
++ serves as a way to assign a value in programming. It must have a valid left-hand-side operand, even if it appears on the right side of the code.
In contrast, [] is simply a value and cannot be used for assignment purposes.
When you encounter [[]][0], it results in an empty array [], but since it points to an element within an existing array, it is considered a valid left-hand-side operand.
Let's clarify with a less complex example:
var x = 1
1++ // This will cause an error
x++ // This will work without issues
The specific behavior in JavaScript arises when you have an expression like +[] + 1, where the empty array gets converted first to an empty string, then explicitly to zero (+"" equals 0), which is then added to 1.
It is important to note that the ++ operator always coerces to a number, unlike the + operator which can be satisfied with an empty string (thus, [] + 1 equates to "" + "1"). Hence, while working with ++, remember to ensure the operands are treated as numbers, although it may not significantly impact your example scenario.
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