/**************************************
* Jonas Raoni Soares Silva
* http://www.joninhas.ath.cx
**************************************/

String.prototype.expandExponential = function(){//v1.0
    return this.replace(/^([+-])?(\d+).?(\d*)[eE]([-+]?\d+)$/, function(x, s, n, f, c){
        var l = +c < 0, i = n.length + +c, x = (l ? n : f).length,
        c = ((c = Math.abs(c)) >= x ? c - x + l : 0),
        z = (new Array(c + 1)).join("0"), r = n + f;
        return s + (l ? r = z + r : r += z).substr(0, i += l ? z.length : 0) + (i < r.length ? "." + r.substr(i) : "");
    });
};

<script type="text/javascript">

document.write(
    '"', s = "-13.441e+5", "\".expandExponential() = ", s.expandExponential(), '<br />',
    '"', s = "1.12300e-1", "\".expandExponential() = ", s.expandExponential(), '<br />',
    "n = ", n = 100000000000000000000000000000000000, " => String(n).expandExponential() = ",
    String(n).expandExponential()
);

</script>