Read/Write bytes of float in JS

Question

Is there any way I can read bytes of a float value in JS? What I need is to write a raw FLOAT or DOUBLE value into some binary format I need to make, so is there any way to

Answer 1

I've created an expansion of Milos' solution that should be a bit faster, assuming TypedArrays are not an option of course (in my case I'm working with an environment where they're not available):

function Bytes2Float32(bytes) {
    var sign = (bytes & 0x80000000) ? -1 : 1;
    var exponent = ((bytes >> 23) & 0xFF) - 127;
    var significand = (bytes & ~(-1 << 23));

    if (exponent == 128) 
        return sign * ((significand) ? Number.NaN : Number.POSITIVE_INFINITY);

    if (exponent == -127) {
        if (significand == 0) return sign * 0.0;
        exponent = -126;
        significand /= (1 << 22);
    } else significand = (significand | (1 << 23)) / (1 << 23);

    return sign * significand * Math.pow(2, exponent);
}

Given an integer containing 4 bytes holding an IEEE-754 32-bit single precision float, this will produce the (roughly) correct Javascript number value without using any loops.