JS Ternary operator confusion

Question

I'm learning about ternary operators now. I got the basics down, but then I saw this snippet and it doesn't make any sense to me. Can anyone please explain how is it put together?!

b.m & 4 || (c |= 2, 63 <= a && 77 >= a ? a = 65 : 48 <= a && 57 >= a ? a = 48 : c & 1 ? 97 <= a && 122 >= a ? a = 65 : 197 == a || 229 == a ? c &= 5 : 192 <= a && 687 >= a ? a = 192 : 1536 <= a ? a = 1536 : 912 <= a ? a = 912 : 160 <= a ? a = 160 : 127 <= a ? c &= 5 : 33 <= a ? a = 59 : c &= 5 : 48 > a ? c &= 5 : 65 > a ? a = 59 : 96 > a ? c &= 5 : 112 > a ? a = 96 : 187 > a ? c &= 5 : a = 59);

b.m & 4 || are bit operations as far as I understood, then (c |= 2, another bit operation, but what does comma mean?!

Then there's 63 <= a && 77 >= a ? a = 65 : 48

which translates to

if(a >= 63 && a <= 77){ a = 65 } else { a = 48; }

and then after that comes <= a && 57 >= a ? a = 48 : c & 1 ? 97 <= a which doesn't make any sense to me at all. because 48 was for the previous statement. Can anyone

man that's a long operation. headache just looking at it. all I can help you with is the [comma operator](https://developer.mozilla.org/en/JavaScript/Reference/Operators/Comma_Operator). — Matt K, Jan 18 '12 at 20:13

Li0liQ · Accepted Answer · 2012-01-18T21:29:55.347

Comma is a separate operator in javascript:

The comma operator evaluates both of its operands (from left to right) and returns the value of the second operand.

You have grasped just a part of expression:

Then there's 63 <= a && 77 >= a ? a = 65 : 48

Actually it is a little bit longer (with some formatting):

63 <= a && 77 >= a
    ? a = 65
    : 48 <= a && 57 >= a
        ? a = 48
        : c & 1
            ? 97 <= a && 122 >= a
                ? a = 65
                : 197 == a || 229 == a
                    ? c &= 5
                    : 192 <= a && 687 >= a
                        ? a = 192
                        : 1536 <= a
                            ? a = 1536
                            : 912 <= a
                                ? a = 912
                                : 160 <= a
                                    ? a = 160
                                    : 127 <= a
                                        ? c &= 5
                                        : 33 <= a
                                            ? a = 59
                                            : c &= 5
            : 48 > a
                ? c &= 5
                : 65 > a
                    ? a = 59
                    : 96 > a
                        ? c &= 5
                        : 112 > a
                            ? a = 96
                            : 187 > a
                                ? c &= 5
                                : a = 59

Trying to rewrite it in if-else fasion will yield the following result:

if (63 <= a && 77 >= a){
    a = 65
} else if (48 <= a && 57 >= a){
    a = 48
} else if (c & 1){
    if (97 <= a && 122 >= a){
        a = 65
    } else if (197 == a || 229 == a){
        c &= 5
    } else if (192 <= a && 687 >= a){
        a = 192
    } else if (1536 <= a){
        a = 1536
    } else if (912 <= a){
        a = 912
    } else if (160 <= a){
        a = 160
    } else if (127 <= a){
        c &= 5
    } else if (33 <= a){
        a = 59
    } else {
        c &= 5
    }               
} else {
    if (48 > a){
        c &= 5
    } else if (65 > a){
        a = 59
    } else if (96 > a){
        c &= 5
    } else if (112 > a){
        a = 96
    } else if (187 > a){
        c &= 5
    } else {
        a = 59
    }
}

Please, pay attention that if-else approach lacks returning value currently, whereas ternary operator does return the value of the last operator executed (this may affect the overall value of boolean expression in parentheses).

Thank you very much!! Yeah i was just trying to understand the beginning, but now it's much easier to understand, thank you!!! — user1002194, Jan 18 '12 at 20:40

score 2 · Answer 2 · edited Apr 13 '17 at 12:40

I prefer to format nested ternary statements like this, so they have a simple, readable structure:

//   (is this true) ? then do this  
//   (is this true) ? then do this  
// (all else fails) : then do this

Following that structure, it would look something like this:

  63 <= a && 77 >= a ? a = 65
: 48 <= a && 57 >= a ? a = 48
:              c & 1 ? /* then go into this indented block below */
                         97 <= a && 122 >= a ? a = 65
:                       197 == a || 229 == a ? c &= 5
:                       192 <= a && 687 >= a ? a = 192
:                                  1536 <= a ? a = 1536
:                                   912 <= a ? a = 912
:                                   160 <= a ? a = 160
:                                   127 <= a ? c &= 5
:                                    33 <= a ? a = 59
                                  /* else */ : c &= 5
:            48 > a ? c &= 5
:            65 > a ? a = 59
:            96 > a ? c &= 5
:           112 > a ? a = 96
:           187 > a ? c &= 5
   /* final else */ : a = 59

score 1 · Answer 3 · answered Jan 18 '12 at 20:42

1

The comma isn't a ternary operator, it allows two expressions to replace one.

But more importantly, that's a mess. Break it down, format it, and comment it. Unless you're golfing, combining all of that into one pile is just abusive.

answered Jan 18 '12 at 20:42

jmoreno

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JS Ternary operator confusion

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