Format javascript number as an actually-readable string

format_human_readable_number.js

// Format javascript number as an actually-readable string
// using different d3.formats for different magnitudes.
// If it's NaN or otherwise not a number (ie a string), pass it through.
// For instance: 
//      0.0000103  -> 10.3µ
//      0.000103   -> 0.000103
//      0.103      -> 0.103
//      10.34      -> 10.3
//      1034       -> 1,034
//      1034.1     -> 1,034.1
//      10341.2    -> 10.3k
//      1034123    -> 1.03M
//      0.000      -> 0
//      "hi mom"   -> "hi mom"
//      undefined  -> undefined
//      null       -> null
// See fiddle at http://jsfiddle.net/ses4j/bua30ko0/
(function () {
    var si_formatter = d3.format(".3s");
    var comma_formatter = d3.format(",.3r");
    var fixed_formatter = d3.format(",f");
    var fixed1_formatter = d3.format(",.1f");

    function isInteger(n) {
        return n === +n && n === (n | 0);
    }

    function format_human_readable_number(value) {
        if (isNaN(value) || value === null)
            return value;
        if (value === 0)
            return 0;
        
        var abs_value = Math.abs(value);
        if (abs_value >= 10000) return si_formatter(value);
        else if (abs_value >= 100) {
            if (isInteger(value)) return fixed_formatter(value);
            else return fixed1_formatter(value);
        } else if (abs_value >= 0.00005) {
            if (isInteger(value)) return fixed_formatter(value);
            else return comma_formatter(value);
        } else return si_formatter(value);
    }

    window.format_human_readable_number = format_human_readable_number;
})();