Switch on ranges of integers in JavaScript [duplicate]

Question

Here is another way I figured it out:

const x = this.dealer;
switch (true) {
    case (x < 5):
        alert("less than five");
        break;
    case (x < 9):
        alert("between 5 and 8");
        break;
    case (x < 12):
        alert("between 9 and 11");
        break;
    default:
        alert("none");
        break;
}

Incrementing on the answer by MarvinLabs to make it cleaner:

var x = this.dealer;
switch (true) {
    case (x < 5):
        alert("less than five");
        break;
    case (x < 9):
        alert("between 5 and 8");
        break;
    case (x < 12):
        alert("between 9 and 11");
        break;
    default:
        alert("none");
        break;
}

It is not necessary to check the lower end of the range because the break statements will cause execution to skip remaining cases, so by the time execution gets to checking e.g. (x < 9) we know the value must be 5 or greater.

Of course the output is only correct if the cases stay in the original order, and we assume integer values (as stated in the question) - technically the ranges are between 5 and 8.999999999999 or so since all numbers in js are actually double-precision floating point numbers.

If you want to be able to move the cases around, or find it more readable to have the full range visible in each case statement, just add a less-than-or-equal check for the lower range of each case:

var x = this.dealer;
switch (true) {
    case (x < 5):
        alert("less than five");
        break;
    case (x >= 5 && x < 9):
        alert("between 5 and 8");
        break;
    case (x >= 9 && x < 12):
        alert("between 9 and 11");
        break;
    default:
        alert("none");
        break;
}

Keep in mind that this adds an extra point of human error - someone may try to update a range, but forget to change it in both places, leaving an overlap or gap that is not covered. e.g. here the case of 8 will now not match anything when I just edit the case that used to match 8.

    case (x >= 5 && x < 8):
        alert("between 5 and 7");
        break;
    case (x >= 9 && x < 12):
        alert("between 9 and 11");
        break;

    switch(this.dealer) {
        case 1:
        case 2:
        case 3:
        case 4:
            // Do something.
            break;
        case 5:
        case 6:
        case 7:
        case 8:
            // Do something.
            break;
        default:
            break;
    }

If you don't like the succession of cases, simply go for if/else if/else statements.

This does not require a switch statement. It is clearer, more concise, faster, and optimises better, to use if else statements...

var d = this.dealer;
if (1 <= d && d <= 11) { // making sure in range 1..11
    if (d <= 4) {
        alert("1 to 4");
    } else if (d <= 8) {
        alert("5 to 8");
    } else {
        alert("9 to 11");
    }
} else {
    alert("not in range");
}

Speed test

I was curious about the overhead of using a switch instead of the simpler if...else..., so I put together a jsFiddle to examine it... http://jsfiddle.net/17x9w1eL/

• Chrome: switch was around 70% slower than if else

• Firefox: switch was around 5% slower than if else

• IE: switch was around 5% slower than if else

• Safari: switch was around 95% slower than if else

Notes:

Assigning to the local variable is optional, especially if your code is going to be automatically optimised later.

For numeric ranges, I like to use this kind of construction...

if (1 <= d && d <= 11) {...}

... because to me it reads closer to the way you would express a range in maths (1 <= d <= 11), and when I'm reading the code, I can read that as "if d is between 1 and 11".

Clearer

A few people don't think this is clearer. I'd say it is not less clear as the structure is close to identical to the switch option. The main reason it is clearer is that every part of it is readable and makes simple intuitive sense.

My concern, with "switch (true)", is that it can appear to be a meaningless line of code. Many coders, reading that will not know what to make of it.

For my own code, I'm more willing to use obscure structures from time to time, but if anyone else will look at it, I try to use clearer constructs. I think it is better to use the constructs for what they are intended.

Optimisation

In a modern environment, code is often going to be minified for production, so you can write clear concise code, with readable variable names and helpful comments. There's no clear reason to use switch in this way.

I also tried putting both constructs through a minifier. The if/else structure compresses well, becoming a single short expression using nested ternary operators. The switch statement when minified remains a switch, complete with "switch", "case" and "break" tokens, and as a result is considerably longer in code.

How switch(true) works

I think "switch(true) is obscure, but it seems some people just want to use it, so here's an explanation of why it works...

A switch/case statement works by matching the part in the switch with each case, and then executing the code on the first match. In most use cases, we have a variable or non-constant expression in the switch, and then match it.

With "switch(true), we will find the first expression in the case statements that is true. If you read "switch (true)" as "find the first expression that is true", the code feels more readable.

If you need check ranges you are probably better off with if and else if statements, like so:

if (range > 0 && range < 5)
{
    // ..
}
else if (range > 5 && range < 9)
{
    // ..
}
else
{
    // Fall through
}

A switch could get large on bigger ranges.

No, this is not possible. The closest you can get is:

  switch(this.dealer) {
    case 1:
    case 2:
    case 3:
    case 4:
                      // DO SOMETHING
        break;
    case 5:
    case 6:
    case 7:
    case 8:
                      // DO SOMETHING
       break;

But this very unwieldly.

For cases like this it's usually better just to use a if/else if structure.