Exhaustiveness checking in switch with union type JS-0383
Anti-pattern
Minor
a month ago
—
3 months old
Switch is not exhaustive. Cases not matched: "flat"
14 let additionalFeeAmount =
15 licenceCategoryAdditionalFee.additionalFeeNumber ?? 0
16
17 switch (licenceCategoryAdditionalFee.additionalFeeType) {18 case 'percent': {
19 additionalFeeAmount = baseLicenceFeeFloat * (additionalFeeAmount / 100)
20 break
Description
Union type may have a lot of parts. It's easy to forget to consider all cases in switch. This rule reminds which parts are missing. If domain of the problem requires to have only a partial switch, developer may explicitly add a default clause.
Bad Practice
type Day =
| 'Monday'
| 'Tuesday'
| 'Wednesday'
| 'Thursday'
| 'Friday'
| 'Saturday'
| 'Sunday';
const day = 'Monday' as Day;
let result = 0;
switch (day) {
case 'Monday': {
result = 1;
break;
}
}
Recommended
type Day =
| 'Monday'
| 'Tuesday'
| 'Wednesday'
| 'Thursday'
| 'Friday'
| 'Saturday'
| 'Sunday';
const day = 'Monday' as Day;
let result = 0;
switch (day) {
case 'Monday': {
result = 1;
break;
}
case 'Tuesday': {
result = 2;
break;
}
case 'Wednesday': {
result = 3;
break;
}
case 'Thursday': {
result = 4;
break;
}
case 'Friday': {
result = 5;
break;
}
case 'Saturday': {
result = 6;
break;
}
case 'Sunday': {
result = 7;
break;
}
}
OR
type Day =
| 'Monday'
| 'Tuesday'
| 'Wednesday'
| 'Thursday'
| 'Friday'
| 'Saturday'
| 'Sunday';
const day = 'Monday' as Day;
let result = 0;
switch (day) {
case 'Monday': {
result = 1;
break;
}
default: {
result = 42;
}
}