Counts the number of significant digits of a number.
Based on the solution provided by @Jos de Jong.
This is part of package extra-number.
number.significantDigits(n);
// n: a numberconst number = require('extra-number');
number.significantDigits(0.0034);
// 2
number.significantDigits(120.5e50);
// 4
number.significantDigits(120.5e-50);
// 4