Shortening a Javascript if-else structure

Question

The code I have is:

 var level = function (d) {
    if (value(d) > median + stdev) {
        return 1;
    } else if (value(d) > median) {
        return 2         


        

Answer 1

I'd recommend to avoid multiple calls to value:

function level(d) {
    var diff = value(d) - median;
    if (diff > 0) {
        if (diff > stdev)
            return 1;
        else
            return 2;
    else
        if (diff > -stdev)
            return 3;
        else
            return 4;
}

Also I've nested the if-else-statements in a (hopefully) more meaningful structure - that depends on your usecase though. Might be more helpful if you returned values like -2, -1, 1 and 2 instead or something. A ternary operator could save you some writing, but it's not necessarily getting clearer.

Alternatively, some maths could help you:

function level(d) {
    var diff = value(d) - median;
    return 2 + (diff > 0 ? -.5 : .5) * (Math.abs(diff) > stdev ? 3 : 1);
}

Though it leads to 3 instead of 4 in case value(d) === median-stdev. See @6502's answer on how to avoid that.