JavaScript if / else if / else语句不起作用

Question

This is my if/else if/ else statement:

var shirtWidth = 18;
var shirtLength = 33;
var shirtSleeve = 8.63;

// Small Shirts
if(shirtWidth >= 18 && shirtWidth < 20) {
        if(shirtLength >= 28 && shirtLength < 29)
        if(shirtSleeve >= 8.13 && shirtSleeve < 8.38) {
            console.log("S");
        }
}
// Medium Shirts
else if(shirtWidth >= 20 && shirtWidth < 22) {
        if(shirtLength >= 29 && shirtLength < 30)
        if(shirtSleeve >= 8.38 && shirtSleeve < 8.63) {
            console.log("M");
        }
}
// Large Shirts
else if(shirtWidth >= 22 && shirtWidth < 24) {
        if(shirtLength >= 30 && shirtLength < 31)
        if(shirtSleeve >= 8.63 && shirtSleeve < 8.88) {
            console.log("L");
        }
}
// XL Shirts
else if(shirtWidth >= 24 && shirtWidth < 26) {
        if(shirtLength >= 31 && shirtLength < 33)
        if(shirtSleeve >= 8.88 && shirtSleeve < 9.63) {
            console.log("XL");
        }
}
// 2XL Shirts
else if(shirtWidth >= 26 && shirtWidth < 28) {
        if(shirtLength >= 33 && shirtLength < 34)
        if(shirtSleeve >= 9.63 && shirtSleeve < 10.13) {
            console.log("2XL");
        }
}
// 3XL Shirts
else if(shirtWidth === 28) {
        if(shirtLength === 34)
        if(shirtSleeve === 10.13) {
            console.log("3XL");
        }
}
// Does not match any shirt sizes
else {
    console.log("N/A");
}

Everything works except when I get to the else statement at the end. It only works for numbers greater than the 3XL shirts. However, if the numbers are combination of measurements from the 6 categories, the else statement does not print. Does anyone know what I am doing wrong?

Answer 1

Consider this part from a logic perspective:

// Small Shirts
if(shirtWidth >= 18 && shirtWidth < 20) {
        if(shirtLength >= 28 && shirtLength < 29)
        if(shirtSleeve >= 8.13 && shirtSleeve < 8.38) {
            console.log("S");
        }
}
else // ...

So if shirtWidth matches that first condition, you branch into the body of the if . But if shirtLength or shirtSleeve don't match the conditions there, you don't do anything. At all. Because the else isn't connected to them. It's connected to the if(shirtWidth >= 18 && shirtWidth < 20) .

Combine your conditions with && and use only a single layer of if s:

// Small Shirts
if (shirtWidth >= 18 && shirtWidth < 20 &&
    shirtLength >= 28 && shirtLength < 29 &&
    shirtSleeve >= 8.13 && shirtSleeve < 8.38) {
    console.log("S");
}
// Medium Shirts
else // ...

---

Having said that, aside from syntax, I suspect the logic of the code isn't quite what you want. What if a shirtWidth is 19 but shirtLength is 30? None of your cases handles that.

Answer 2

TJ Crowder's answer is perfect (and should be accepted), but I might suggest separating your conditions to make it easier to read and manage:

 var shirtWidth = 18; var shirtLength = 33; var shirtSleeve = 8.63; var isSmall = shirtWidth >= 18 && shirtWidth < 20 && shirtLength >= 28 && shirtLength < 29 && shirtSleeve >= 8.13 && shirtSleeve < 8.38; var isMedium = shirtWidth >= 20 && shirtWidth < 22 && shirtLength >= 29 && shirtLength < 30 && shirtSleeve >= 8.38 && shirtSleeve < 8.63; var isLarge = shirtWidth >= 22 && shirtWidth < 24 && shirtLength >= 30 && shirtLength < 31 && shirtSleeve >= 8.63 && shirtSleeve < 8.88; var isXL = shirtWidth >= 22 && shirtWidth < 24 && shirtLength >= 31 && shirtLength < 33 && shirtSleeve >= 8.88 && shirtSleeve < 9.63; var isXXL = shirtWidth >= 26 && shirtWidth < 28 && shirtLength >= 33 && shirtLength < 34 && shirtSleeve >= 9.63 && shirtSleeve < 10.13; var is3XL = shirtWidth === 28 && shirtLength === 34 && shirtSleeve === 10.13; if(isSmall) { console.log("S"); } else if(isMedium) { console.log("M"); } else if(isLarge) { console.log("L"); } else if(isXL) { console.log("XL"); } else if(isXXL) { console.log("2XL"); } else if(is3XL) { console.log("3XL"); } else {// Does not match any shirt sizes console.log("N/A"); } 

Answer 3

You will need to add a return statement at each console.log statement or combine the if conditions using the && operator.

var shirtWidth = 18;
var shirtLength = 33;
var shirtSleeve = 8.63;

// Small Shirts
if (shirtWidth >= 18 &&
    shirtWidth < 20 &&
    shirtLength >= 28 &&
    shirtLength < 29 &&
    shirtSleeve >= 8.13 &&
    shirtSleeve < 8.38) {
    console.log("S");
}
// Medium Shirts
else if (shirtWidth >= 20 &&
    shirtWidth < 22 &&
    shirtLength >= 29 &&
    shirtLength < 30 &&
    shirtSleeve >= 8.38 &&
    shirtSleeve < 8.63) {
    console.log("M");
}
// Large Shirts
else if (shirtWidth >= 22 &&
    shirtWidth < 24 &&
    shirtLength >= 30 &&
    shirtLength < 31 &&
    shirtSleeve >= 8.63 &&
    shirtSleeve < 8.88) {
    console.log("L");
}
// XL Shirts
else if (shirtWidth >= 24 &&
    shirtWidth < 26 &&
    shirtLength >= 31 &&
    shirtLength < 33 &&
    shirtSleeve >= 8.88 && shirtSleeve < 9.63) {
    console.log("XL");
}
// 2XL Shirts
else if (shirtWidth >= 26 &&
    shirtWidth < 28 &&
    shirtLength >= 33 &&
    shirtLength < 34 &&
    shirtSleeve >= 9.63 &&
    shirtSleeve < 10.13) {
    console.log("2XL");
}
// 3XL Shirts
else if (shirtWidth === 28 &&
    shirtLength === 34 &&
    shirtSleeve === 10.13) {
    console.log("3XL");

}
// Does not match any shirt sizes
else {
    console.log("N/A");
}

Not the best possible way to do this, but this should solve your problem.

Answer 4

This is what I ended up doing:

var shirtWidth = 24;
var shirtLength = 28;
var shirtSleeve = 10;

// Small Shirts
if(shirtWidth >= 18 && shirtWidth < 20 &&
    shirtLength >= 28 && shirtLength < 29 &&
    shirtSleeve >= 8.13 && shirtSleeve < 8.38) {
        console.log("S");
    }
// Medium Shirts
else if(shirtWidth >= 20 && shirtWidth < 22 &&
    shirtLength >= 29 && shirtLength < 30 &&
    shirtSleeve >= 8.38 && shirtSleeve < 8.63) {
        console.log("M");
    }
// Large Shirts
else if(shirtWidth >= 22 && shirtWidth < 24 &&
    shirtLength >= 30 && shirtLength < 31 &&
    shirtSleeve >= 8.63 && shirtSleeve < 8.88) {
        console.log("L");
    }
// XL Shirts
else if(shirtWidth >= 24 && shirtWidth < 26 &&
    shirtLength >= 31 && shirtLength < 33 &&
    shirtSleeve >= 8.88 && shirtSleeve < 9.63) {
        console.log("XL");
    }
// 2XL Shirts
else if(shirtWidth >= 26 && shirtWidth < 28 &&
    shirtLength >= 33 && shirtLength < 34 &&
    shirtSleeve >= 9.63 && shirtSleeve < 10.13) {
        console.log("2XL");
    }
// 3XL Shirts
else if(shirtWidth === 28 &&
    shirtLength === 34 &&
    shirtSleeve === 10.13) {
        console.log("3XL");
    }
// Does not match any shirt sizes
else {
    console.log("N/A");
}