Multiple 'If' statements?

问题:

Assume i have a function checkTime like the one below where i have to check for multiple condition simultaneously.

var result=0;
function checkTime(time1, time2) {

    if (time1 >= 0 && time2 <= 0) {
        result = 1;
    }
    else if (time1 >= 0 && time2 <= 1) {
        result = 4;
    }
    else if (time1 >= 2 && time2 <= 3) {
        result = 5;
    }
    else if (time1 >= 4 && time2 <= 6) {
        result = 6;
    }
    else if (time1 >= 7 && time2 <= 9) {
        result = 7;
    }
    else if (time1 >= 11 && time2 <= 12) {
        result = 8;
    }
    else if (time1 >= 13 && time2 <= 15) {
        result = 9;
    }
    else if (time1 >= 16 && time2 <= 17) {
        result = 10;
    }
    else if (time1 >= 19 && time2 <= 20) {
        result = 11;
    }
    return result;
}

(The above given example is hypothetical)

The function i have used totally works,but:

• Is there a better method or procedure or formula to replace this?(where it doesnt have to be this lengthy or ugly)

Thanx!

回答1:

You can use an array to represent all the combination:

tests = [
    { time1: 0, time2: 0, result: 1 },
    { time1: 0: time2: 1, result: 4 },
    ...
];

for (var i = 0; i < tests.length; i++) {
    if (time1 >= tests[i].time1 && time2 <= tests[i].time2) {
        return tests[i].result;
    }
}

回答2:

If the code is identical, and only the values change, you could do something like this:

function checkTime(time1, time2) {
  [
    [0, 0, 0], 
    [0, 1, 0]
  ].forEach(function (it) {
    if (time1 >= it[0] && time2 <= it[1]) {
       return it[2];
    }
  });
}

回答3:

Well, first off you have the possibility of an undefined result, so that makes things ambiguous. Should result start at 0 instead? This is an important detail. Second, you seem to be working with boundaries, so it would help to change the <= to < to make this clearer. (If so, the 7-9/11-12 section has a bug.) Third, you have an implicit comparison of time1 and time2, so make that explicit.

var result = 0;
var diff = time2 - time1;
var bounds = [21, 19, 16, 13, 11, 7, 4, 2, 0];
if (diff <= 0) result = 0; // unexpected outcome
else
    for (position = 1; position < bounds.length; ++position) {
        if (time1 >= bounds[position]) {
            if (time2 < bounds[position - 1]) {
                result = 3 + (bounds.size - position);
            }
            break;
        }
    }
return result;

Other implementations are possible, but it's hard to tell based on your question exactly what problem you're solving.

follow-up

This section of code has a gap:

else if (time1 >= 7 && time2 <= 9) {
    result = 7;
}
else if (time1 >= 11 && time2 <= 12) {
    result = 8;
}

If time = 10 and time2 = 10, there is no match. It's easy to miss this type of error when you are repeating yourself. Specifying lower and upper bounds for each condition is unnecessary repetition. Since I couldn't see a pattern to the bounds (which could be delegated to a function), I just put the lower bounds into an array and made sure it was sorted descending so that the loop could stop after the first match.