TS1130: 'case' or 'default' expected

TypeScript is a strongly typed programming language that builds on JavaScript by adding static types. This means that in TypeScript, you can define data types for variables, function parameters, and return values, which helps improve code quality and catch errors at compile time. Types in TypeScript can include basic types like number, string, and boolean, as well as more complex structures like interfaces, enums, and generics.

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Understanding Enums

Enums are a special type in TypeScript that allow you to define a set of named constants. They are helpful for creating a clear and manageable way to handle sets of related values. For instance, you can represent a collection of states for a network request (like Loading, Success, and Error) using enums.

Here's how you can define an enum in TypeScript:

enum RequestState {
    Loading,
    Success,
    Error
}

// Using enums
let currentState: RequestState = RequestState.Loading;

TS1130: 'case' or 'default' expected.

One common error you can encounter while working with TypeScript is the TS1130: 'case' or 'default' expected. This error typically arises in a switch statement when TypeScript expects either a case label or a default clause but fails to find one.

Here’s an example that triggers the TS1130 error:

const value = 2;

switch (value) {
    case 1:
        console.log("Value is 1");
        break;
    // Missing case or default here
}

In this example, TypeScript recognizes that the switch statement contains a case label, but it should either terminate or include another case or a default label. To fix this error, you must either provide additional cases or include a default case.

Here’s the corrected version:

const value = 2;

switch (value) {
    case 1:
        console.log("Value is 1");
        break;
    case 2:
        console.log("Value is 2");
        break;
    default:
        console.log("Value is unknown");
}

Important to know!

1. TypeScript Errors: TS1130 errors emphasize the need for proper case handling in switch statements.
2. Structure: Every switch statement must contain at least one case or a default clause to be valid.

FAQ's

Q: What is a switch statement in TypeScript?
A: A switch statement is used for conditional logic, allowing for multiple conditional branches based on the value of a variable.

Q: How can I troubleshoot TS1130 errors?
A: Check the structure of your switch statements to ensure there are appropriate case labels or a default clause.

Conclusion

In summary, the TS1130: 'case' or 'default' expected error is a reminder to maintain proper structure in your switch statements within TypeScript. Always ensure that cases are well defined, and remember that every switch statement should conclude either with a case or a default label. Practice will help reinforce these structures, and using tools like gpteach can provide guidance and learning opportunities. Happy coding!