JsHint：“期望分配或函数调用，而是看到一个表达式”，Switch语句

Question

Consider this code and output:

var f = function(x){
switch(x){
    case 1:
        3 + 2 > 3 && (console.log("case 1"));
        break;
    case 2:
        4 + 2 < 20 && (console.log("case 2"));
        break;
    case 3:
        true && console.log("case 3");
        break;
    case 4:
        false && console.log("case 4");
}

};

for(var i = 0; i < 6; i++){
    f(i)
    }

Output:

case 1
case 2
case 3

I get a complaint from JsHint saying

"Expected an assignment or function call and instead saw an expression"

for line 4, 7, 10 and 13. That is for each line containing "&&". I managed to escape this by using functions within the Switch statement, for example:

case1:
    function a() {3 + 2 > 3 && (console.log("case 1"))}
    a()
    break;

etc.

I wonder why JsHint makes this warning and if there is a better way to solve the problem with the warnings?

Answer 1

Keep in mind that JSHint is just the embodiment of a set of opinions about what "good" code is like. Here, it's essentially telling you that it disapproves of your use of the && operator for control flow. You could probably make it happy by switching to a simple if statement:

case 1:
    if (3 + 2 > 3) console.log("case 1");
    break;

Answer 2

A switch statement is, logically, like multiple If/Else statements.

So:

 switch(x){
    case 1:
        3 + 2 > 3 && (console.log("case 1"));
        break;
    case 4:
        false && console.log("case 4");
 }

is the equivalent of:

if (x == 1){
    3 + 2 > 3 && (console.log("case 1"));
} else if (x == 4) {
    false && console.log("case 4");
}

As you might be able to see, simply using a logical condition doesn't generally make sense. You usually want to actually do something, eg assignment or function. JSHint is warning you of a likely mistake.