I am using Javascript in Firefox (version 77), and I have a few console.log statements to observe some values that are not being set correctly. If I view the variables they somehow get fixed, but then I get an error! If I don't view them, the program runs without a hitch, but gets the values wrong!
The program was large, but after reducing to MWE, it is extremely simple. Here it is:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script type="text/javascript">
function draw() {
function quad(A, B) {
console.log(A, B)
return [1,2,3]
}
let A = [5, 5]
let B = [105, 5]
let [C, D, E] = quad(A, B)
A = [110, 5]
B = [210, 5]
console.log(B) // This is line 18
[C, D, E] = quad(A, B)
console.log(C,D,E)
}
</script>
</head>
<body onload="draw();">
</body>
</html>
The behavior is as follows:
If I run it as it is, I get the expected output, and then it has an error. The output is
Array [5, 5 ] Array [ 105, 5 ]
Array [210, 5]
Array [110, 5] Array [ 210, 5 ]
and the error is
Line 19:16 has error: TypeError: console.log(...) is undefined
On the other hand, if I comment line 18, I get no error, but the wrong output
Array [5, 5 ] Array [ 105, 5 ]
Array [110, 5] Array [ 105, 5 ]
1 2 3
The second array in the middle line should be [210, 5], because that is what it was set to just moments ago.
It appears that it has something to do with the multiple assignments, because when I replaced C,D,E with a single variable, then it started to work.
