float numbers formatting

float.js

const float = function(v, p=2){
	let absv = Math.abs(v);
	if (absv>10**(p+3) || absv<10**-p) return v.toExponential(p).replace(/0+e/, 'e');
	return v.toFixed(p).replace(/\.0+$|0+$/, '');
}

// run the following to test the float function and
// compare the values with common formatting functions

const bodys = [
	"v.toString()",
	"v.toFixed(3)",
	"v.toExponential(3)",
	"v.toPrecision(3)",
	"float(v, 2)",
	"float(v, 3)",
];
const funs = bodys.map(b=>(v=>eval(b)));
const tests = [
	1, 12, 123, 1234, 12345, 123456, 1234567, 123456789, 1234567890,
	.1, .12, .123, .1234,
	100, 100.1, 100.01, 100.001, 100.0001, 100.00001,
	1.99, 1.999, 1.9999, 1.99999999,
	.047, .0047, .00047, .000047, .000000047, .0000000000000047,
	NaN
];
[bodys, bodys.map(_=>"-:")].concat(tests.map(t=>
	funs.map(f=>f(t))
)).forEach(row => console.log(row.map(c=>c.padStart(20, " ")).join(" | ")));

result.txt

        v.toString() |         v.toFixed(3) |   v.toExponential(3) |     v.toPrecision(3) |          float(v, 2) |          float(v, 3)             
                   1 |                1.000 |             1.000e+0 |                 1.00 |                    1 |                    1             
                  12 |               12.000 |             1.200e+1 |                 12.0 |                   12 |                   12             
                 123 |              123.000 |             1.230e+2 |                  123 |                  123 |                  123             
                1234 |             1234.000 |             1.234e+3 |              1.23e+3 |                 1234 |                 1234             
               12345 |            12345.000 |             1.235e+4 |              1.23e+4 |                12345 |                12345             
              123456 |           123456.000 |             1.235e+5 |              1.23e+5 |              1.23e+5 |               123456             
             1234567 |          1234567.000 |             1.235e+6 |              1.23e+6 |              1.23e+6 |             1.235e+6             
           123456789 |        123456789.000 |             1.235e+8 |              1.23e+8 |              1.23e+8 |             1.235e+8             
          1234567890 |       1234567890.000 |             1.235e+9 |              1.23e+9 |              1.23e+9 |             1.235e+9             
                 0.1 |                0.100 |             1.000e-1 |                0.100 |                  0.1 |                  0.1             
                0.12 |                0.120 |             1.200e-1 |                0.120 |                 0.12 |                 0.12             
               0.123 |                0.123 |             1.230e-1 |                0.123 |                 0.12 |                0.123             
              0.1234 |                0.123 |             1.234e-1 |                0.123 |                 0.12 |                0.123             
                 100 |              100.000 |             1.000e+2 |                  100 |                  100 |                  100             
               100.1 |              100.100 |             1.001e+2 |                  100 |                100.1 |                100.1             
              100.01 |              100.010 |             1.000e+2 |                  100 |               100.01 |               100.01             
             100.001 |              100.001 |             1.000e+2 |                  100 |                  100 |              100.001             
            100.0001 |              100.000 |             1.000e+2 |                  100 |                  100 |                  100             
           100.00001 |              100.000 |             1.000e+2 |                  100 |                  100 |                  100             
                1.99 |                1.990 |             1.990e+0 |                 1.99 |                 1.99 |                 1.99             
               1.999 |                1.999 |             1.999e+0 |                 2.00 |                    2 |                1.999             
              1.9999 |                2.000 |             2.000e+0 |                 2.00 |                    2 |                    2             
          1.99999999 |                2.000 |             2.000e+0 |                 2.00 |                    2 |                    2             
               0.047 |                0.047 |             4.700e-2 |               0.0470 |                 0.05 |                0.047             
              0.0047 |                0.005 |             4.700e-3 |              0.00470 |               4.7e-3 |                0.005             
             0.00047 |                0.000 |             4.700e-4 |             0.000470 |               4.7e-4 |               4.7e-4             
            0.000047 |                0.000 |             4.700e-5 |            0.0000470 |               4.7e-5 |               4.7e-5             
              4.7e-8 |                0.000 |             4.700e-8 |              4.70e-8 |               4.7e-8 |               4.7e-8             
             4.7e-15 |                0.000 |            4.700e-15 |             4.70e-15 |              4.7e-15 |              4.7e-15             
                 NaN |                  NaN |                  NaN |                  NaN |                  NaN |                  NaN