How to Convert a String to enum in TypeScript?

In TypeScript, an enum is a type of class that is mainly used to store the constant variables with numerical and string-type values. In this article, we will learn, how we can convert a string into an enum using TypeScript.

These are the two approaches that can be used to solve it:

Using custom mapping

In this approach, we will define an enum initialized with string values and then map through each item to compare them with a string and return the matching enum value to convert the string into an enum.

Example: The below example will explain how you can convert a string into an enum using custom mapping.

Javascript

enum GFG {
    name = "GeeksforGeeks",
    desc = "A Computer Science portal."
}

// Function to convert string into enum
function convertStrToEnum(convertingStr: string):
    GFG | string {
    switch (convertingStr) {
        case "GeeksforGeeks":
            return GFG.name;
        case "A Computer Science portal.":
            return GFG.desc;
        default:
            return `Pass either "${GFG.name}" or "${GFG.desc}" 
            as testing string to the function`;
    }
}

console.log(convertStrToEnum("GeeksforGeeks"));
console.log(convertStrToEnum("TypeScript"));
console.log(convertStrToEnum("A Computer Science portal."));

Output:

GeeksforGeeks
Pass either "GeeksforGeeks" or "A Computer Science portal." as testing string to the function
A Computer Science portal.

Using the keyof and typeof operators together

The keyof and the typeof operators can together be used to convert an string into an enum in TypeScript.

Syntax:

const variable_name: keyof typeof enum_name = value;

Example: The below example will explain the use of the keyof and typeof operators to convert a string into an enum.

Javascript

enum GFG {
    name = 25,
    desc = 56
}

// Converting string to enum
const myStr: keyof typeof GFG = 'name';
const myStr1: keyof typeof GFG = 'desc';

// It prints 25, as the string is now converted
// to the value of first constant of enum
console.log(GFG[myStr]);

// It prints 56, as the string is now converted
// to the value of second constant of enum
console.log(GFG[myStr1]);

Output:

25
56

Using type assertion

In this method, we will convert a string to an enum by using the unknown type assertion at the time of conversion.

Syntax:

const variable_name1: string = value_as_enum_key_as_string;
const variable_name2 = variable_name1 as unknown as enum_name;

Example: The below code example illustrate the type assertion approach to convert a string into enum using TypeScript.

Javascript

enum GFG {
    num1 = 28,
    num2 = 56,
    num3 = 84
}

// Assigning enum values to 
// string type variables
const str1: string = 'num1';
const str2: string = 'num2';
const str3: string = 'num3';

// Converting String into enum
const str1ToEnum = str1 as unknown as GFG;
const str2ToEnum = str2 as unknown as GFG;
const str3ToEnum = str3 as unknown as GFG;

console.log(GFG[str1ToEnum]);
console.log(GFG[str2ToEnum]);
console.log(GFG[str3ToEnum]);

Output:

28
56
84

Using a generic function

In this approach, we’ll create a generic function that ensures type safety during the conversion of a string to an enum. The function checks if the provided string matches any of the enum values and returns the corresponding enum value or a message indicating the valid options.

Syntax:

function convertStrToEnum<T extends keyof typeof enum_name>(convertingStr: string): enum_name | 
string {
    // Implementation
}

Example: The following example demonstrates the usage of a generic function approach to convert a string into an enum.

JavaScript

enum GFG {
    name = "GeeksforGeeks",
    desc = "A Computer Science portal."
}

// Generic function to convert string into enum
function convertStrToEnum<T extends keyof typeof GFG>(convertingStr: string): GFG 
| string {
    if (Object.values(GFG).includes(convertingStr as GFG)) {
        return convertingStr as GFG;
    } else {
        return `Pass either "${GFG.name}" or 
        "${GFG.desc}" as testing string to the function`;
    }
}

console.log(convertStrToEnum("GeeksforGeeks")); 
console.log(convertStrToEnum("TypeScript")); 
console.log(convertStrToEnum("A Computer Science portal."));

Output:

GeeksforGeeks
Pass either "GeeksforGeeks" or "A Computer Science portal." as testing string to the function
A Computer Science portal.