const values = ['0.000002', '-0.000007', '0.000026', '-0.000043', '-0.000029', '-0.000021', '-0.000023'];
The objective here is to find a positive number that can be added to each of the items in the array to make them all positive. Hence, the best way to proceed is to find the most negative number in the array. This is done by first mapping all of the stringified numbers into number form. Then, the positive numbers are filtered out. Next, the array is sorted in ascending order. Finally, the first item in the array is the most negative number.
const mostNegativeNumber = values.map(value => +value)
.filter(value => value < 0)
.sort((x, y) => x - y)
.shift();
The answer here is any number that is greater than the opposite of this negative number.
console.log(`Add any number that is greater than ${-mostNegativeNumber}.`);