I have the following array:
let array = [1, 2, 3, [(4, 5, [(6, 7, 8)], 9, [10])]];
I'm using recursion to loop through and reduce it down to a single array.
To start, I just want to console.log(array) within the for loop. So code is:
function reduceArray(array) {
for (let i = 0; i < array.length; i++) {
console.log(array[i])
}
}
Expecting to see 4 elements of:
1
2
3
[(4, 5, [(6, 7, 8)], 9, [10])]
I instead get:
1
2
3
[10]
What's happening here?
You have parens (), which you seem to assume do nothing, but they actually do have meaning in JS and most languages. Here, the ()'s mean the , is interpreted as comma operators instead of as delimiters for arrays.
3 evaluates to 3, simple enough.[3, 4] interprets the , as an array delimiter and evaluates to an array with 2 elements.(x(), 3, 5) interprets the , as the comma operator and evaluates to 5, but also invokes x(), which may have side affects.[3, (x(), 6)] interprets the 1st , as an array delimiter, interprets the 2nd , as the comma operator, and evaluates to [3, 6], but also invokes x().Here's another example:
let y = 10;
let incY = () => y++;
console.log((incY(), incY(), y));So returning to your example, when you have [(4, 5, [(6, 7, 8)], 9, [10])], that evaluates to [10].
The comma operator (,) simply evaluates both of its operands and returns the value of the last operand. MDN, comma operator
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