Typescript Convert String/Number to Enum example

Typescript Convert String/Number to Enum example

The enum contains both string and number properties. Converting from a string or number to an enum isn’t automatic and lacks a built-in method. This post discusses parsing strings or numbers to and from an enum, providing examples.

You can check my other posts on typescript Enum object

Let’s declare the Month enum, which holds properties of strings only. We’ll utilize this enum object throughout this tutorial.

export enum Month {
  JAN,
  FEB,
  MAR,
  APR,
  MAY,
  JUN,
}
console.log(MONTH);

How to Convert String to Enum in TypeScript?

We’ve created a Month enum with strings.

There are multiple ways to convert to Enum object from a string

  • using Enum[string] Syntax

    To retrieve an enum object for a given string, use the syntax Enum[string]. In this case, the Month enum accepts string values and returns an Enum object. Since enum properties are strongly typed, this approach thrown an error if --noImplicitAny is enabled, .

    // To Enum/number
var month: Month = Month["JAN"];

  • using keyof & typeof Another approach, especially when the --noImplicitAny configuration is enabled, involves retrieving enum string information using keyof and typeof, then casting the string with keyof typeof` to return the Enum object.

    const str = "FEB";
let  month1:Month= <keyof typeof Month> str;

convert Number to Enum

Enums without explicitly assigned values are automatically assigned values starting from 0, 1, 2, and so on.

Here’s a convertNumberToEnum() method that accepts a Month object and a number. This method checks if the number corresponds to a valid enum object. If not, it returns undefined. The Month enum also provides mappings and reverse mappings of its values.

If you print an enum object, the following are the values.

// mapping data - names to values
JAN-0
FEB-1
MAR-2
APR-3
MAY-4
JUN-5
// Reverse mapping data - values to names
0-JAN,
1-FEB,
2-MAR,
3-APR,
4-MAY,
5-JUN

At runtime, the Enum object can be retrieved using the following code to parse a number into an enum object in TypeScript.

Here is the code for parse number to enum object in typescript

private convertNumberToEnum(object: Month, x:number): Month{
    if (typeof object[x] === 'undefined') {
        console.log('Invalid Enum number');
        return undefined;
    }
    return object;
}
console.log(convertNumberToEnum(Month,1))//FEB

Conclusion

In summary, you have learned various approaches to converting a string or a number into an corresponding Enum object.