Numbers Precision

precision.js

/*

three sgnificant figures for large numbers expressed using power of ten suffixes "k", "M" and "B". Ex: 12.3k, 1.45m, 534k
For sub 1000 and > 0 numbers, use 4 significant figures - ex: 12.34, 1.234, 123.4
For numbers above 10B, use scientific notation of the form 1.23x10^11
For numbers < 0.001, use scientific notation of the form 1.23x10^-5
For numbers in range 0.001 < n < 1.0, use 3 decimal places - ex: 0.123

*/

const precision = (() => {
  const B = 1e9, M = 1e6, K = 1e3;
  const precisionTypes = [
    { limit: 1, range: K, suffix: '', sig: 4 },
    { limit: K, range: M, suffix: 'k', sig: 3 },
    { limit: M, range: B, suffix: 'm', sig: 3 },
    { limit: B, range: 1e10, suffix: 'b', sig: 3 },
  ];

  const EXPONENT_PATTERN = /(?:\.0+)?e\+?/;

  return (num) => {
    let numeric, decimal, types = precisionTypes, r;
    const sign = num < 0 ? '-' : '';
    num = Math.abs(num);

    if (!num || typeof num !== 'number') { return sign + num; }

    // num < 0.001 or num > 10B
    if (num > 1e10 || num < 1e-3) {
      if (num | 0 === num && num > -1e3 && num < 0) {
        return sign + num;
      }
      return sign + num.toExponential(2)
                .replace(EXPONENT_PATTERN, '⨯10^');
    }

    // 0.001 < num < 1.0
    if (num < 1) {
      return sign + num.toFixed(3);
    }

    if ((num | 0) === num && num < 10 * K) {
     return sign + num;
    }
    
    for (r = 0; r < types.length; r++) {
      if (num < types[r].range) {
        if (num >= K) {
          num = num | 0;
          num = num / types[r].limit;
        }
        numeric = num | 0;
        decimal = num - numeric;
        if (decimal) {
          return  sign + ((numeric + decimal).toFixed(types[r].sig - ("" + numeric).length))
                          + types[r].suffix;
        }
        return sign + numeric + types[r].suffix;
      }
    }
  }
})();

let data = [
  -1, -0.00234533,
  0, 10, 99, 999,
  99.123, 9.12345, 199.2,
  678.234, 123456789012,
  1000, 1001, 99892,
  12345678, 1234567890
];

data.forEach(function(d) {
  console.log(d, precision(d))
})

~ ₹ node test.js
-1 '-1'
-0.00234533 '-2.35⨯10^-3'
0 '0'
10 '10'
99 '99'
999 '999'
99.123 '99.12'
9.12345 '9.123'
199.2 '199.2'
678.234 '678.2'
123456789012 '1.23⨯10^11'
1000 '1k'
1001 '1k'
99892 '99.9k'
12345678 '12.3m'
1234567890 '1.23b'