How to Require a Specific String in TypeScript Interface ?
Last Updated :
24 Apr, 2025
To require a specific string in the TypeScript interface, we have different approaches. In this article, we are going to learn how to require a specific string in the TypeScript interface.
Below are the approaches used to require a specific string in the TypeScript interface:
Approach 1: Using String Literal Type
This approach utilizes string literal types in TypeScript interfaces to define a property with specific allowed string values. In the below example,
- Interface Definition (
TaskStatus):- The
TaskStatus interface is defined with a property named status. - The
status property is restricted to having one of three specific string values: "todo", "in-progress", or "done" using string literal types.
- Valid Object (
task1):- An object
task1 is created with the status property set to a valid value, "todo". - The TypeScript compiler allows this object because "todo" is one of the specified string values in the interface.
Example: Here, the TaskStatus interface restricts the status property to the string values "todo", "in-progress", or "done".
JavaScript
// Using String Literal Type
interface TaskStatus {
status: "todo" | "in-progress" | "done";
}
// Valid object
const task1: TaskStatus = { status: "todo" };
console.log(task1.status); // Output: "todo"
Output:
todo
Approach 2: Using Enum
Enums provide a way to define a set of named constant values. In this approach, an enum is used to create a set of allowed string values for a property in an interface. In the below example,
- Enum Definition (
Weekday):- An enum named
Weekday is defined, where each enum member is assigned a specific string value representing days of the week.
- Interface Definition (
Schedule):- The
Schedule interface is defined with a property named day. - The
day property is restricted to having one of the enum values from Weekday.
- Valid Object (
meeting):- An object
meeting is created with the day property set to a valid enum value, Weekday.Wednesday. - The TypeScript compiler allows this object because
Wednesday is a valid enum value.
Example: Here, the Weekday enum is used to restrict the day property in the Schedule interface to specific string values.
JavaScript
// Using Enum
enum Weekday {
Monday = "Monday",
Tuesday = "Tuesday",
Wednesday = "Wednesday",
Thursday = "Thursday",
Friday = "Friday",
}
interface Schedule {
day: Weekday;
}
// Valid object
const meeting: Schedule = { day: Weekday.Wednesday };
console.log(meeting.day); // Output: "Wednesday"