Enum

An enum may give you additional benefits, if you want the features:

const enum FieldNamesEnum {

  FirstField = Field One,

  SecondField = Field Two

};



let x: FieldNamesEnum;



x = FieldNamesEnum.FirstField;

x = FieldNamesEnum.SecondField;



// Error - not assignable to FieldNames

x = 'str';



// Cannot assign

FieldNamesEnum.FirstField = 'str';

Importantly, you can't assign to the enum members and types are checked to the enum members, rather than string.

Additionally, because you have used a const enum in your example, the enum won't exist at runtime and all the references will be substituted for the literal values (if you used a plain enum the enum would exist at runtime).

Object

Compare this to the object example:

const FieldNames = {

  FirstField: Field One,

  SecondField: Field Two

};



let y: string;



y = FieldNames.FirstField;

y = FieldNames.SecondField;



// Oops it works

y = 'str';



// Oops it works



FieldNames.FirstField = 'str';

Union

If you don't need the full enum, but want to limit the values, you can use a union of literal values:

type FieldNames = Field One | Field Two;



let x: FieldNames;



x = Field One;

x = Field Two;



// Error - not allowed

x = Field Three;