简化此条件语句

Question

I have this crazy conditional that I just know there is a better way to write. Here is the pseudo code:

if( A && B ){
   console.log( 'do not show' );
}

if( A && C ){
   console.log( 'show' );
}

if( A && D ){
   console.log( 'do not show' );
}

if( A && E ) {
   console.log( 'do not show' );
}

I'm just really blanking out.

Answer 1

How about this:

if (A) {
   if (B || D || E) {
     console.log( 'do not show' );
   } 
   if ( C ) {
     console.log( 'show' );
   }
}

If you really wanted to specify separate tasks for each condition, then you could use this, but it's overly complicated if your task is just the above code.

var A = C = true;
var B = D = E = false;

function doWhen( cond, fn ) {
    if ( cond === true ) {
        return ( typeof fn === 'function' ? fn() : fn );
    }
    return undefined;
}

doWhen(A, function() {
    [ [B, function() { console.log('b message') }], 
      [C, function() { console.log('c message') }], 
      [D, function() { console.log('d message') }], 
      [E, function() { console.log('e message') }] ]
        .forEach(function(cond) {
            doWhen.apply(null, cond);
        });
});

Answer 2

Wouldn't this do it:

if (A) {
    if(B || D || E){
       console.log( 'do not show' );
    }

    if( C ){
       console.log( 'show' );
    }
}

update

Or just for fun (if you want every state)

switch((a << 0) | (b << 1) | (c << 2) | (d << 3) | (e << 4)) {
    case 3: console.log("A && B"); break;
    case 5: console.log("A && C"); break;
    case 9: console.log("A && D"); break;
    case 17: console.log("A && E"); break;
}

A JSFiddle to play with: http://jsfiddle.net/LxvBZ/

Answer 3

If you really needed to evaluate B , C , D , and E separately, this is pretty straight forward:

if( A ){
    if( B ){
       console.log( 'do not show' );
    }

    if( C ){
       console.log( 'show' );
    }

    if( D ){
       console.log( 'do not show' );
    }

    if( E ) {
       console.log( 'do not show' );
    }
}

Now if all those if 's (after the first) were supposed to be else if 's, then this can be simplified to:

if( A ){
    if( B || D || E ){
       console.log( 'do not show' );
    }else if( C ){
       console.log( 'show' );
    }
}

Answer 4

I would do:

if ( A ) {
    if( B || D || E ){
       console.log( 'do not show' );
    }

    if( C ){
       console.log( 'show' );
    }
}

Answer 5

if( A ){
    var printOnLog = '';
    if( B || C || E ){
       printOnLog = 'do not show';
    }

    else if( C ){
       printOnLog = 'show';
    }

    else {
      //default action
    }

   console.log(printOnLog);
}

Well, I think that it's impossible to have multiple conditions, if this is true use "else if" to avoid usless if.

If it's possible (A && B) && (A && C), just use normal "if"

Answer 6

You could do this:

if (A) {
    if (C) {
        console.log("show");
    }
    else if (B || D || E) {
        console.log("do not show");
    }
 }

or this if you prefer:

if (A && C) {
    console.log("show");
}
else if (A && (B || D || E)) {
    console.log("do not show");
}

Answer 7

Well, a ternary operator is kind of the same thing. You could use it to shrink the code.

To add more conditions to the ternary operator, use ' ? ' to specify if conditions and ' : ' for specifying else conditions. It has to end with a final else condition however, like shown below.

var output = ((A && B) || (A && D) || (A && E)) ? "do not show" : (A && C) ? "show" : "";
console.log(output);