ES6 read-only enums that can map value to name

Question

I would like to define an enum-like structure in JS, but have two requirements:

1. The values be read-only, i.e. no users can assign to them.
2. The values (0, 1

Answer 1

Just recently implemented an Es6 version that works quite well:

const k_VALUES = {}

export class ErrorCode {

    constructor(p_apiCode, p_httpCode){
        this.apiCode = p_apiCode;
        this.httpCode = p_httpCode;

        k_VALUES[p_apiCode] = this;
    }


    static create(p_apiCode){
        if(k_VALUES[p_apiCode]){
            return k_VALUES[p_apiCode];
        }

        return ErrorCode.UNKNOWN;
    }
}

ErrorCode.UNKNOWN                 = new ErrorCode(0,     500);
ErrorCode.NOT_FOUND               = new ErrorCode(-1000, 404);
ErrorCode.NOT_FOUND_EMAIL         = new ErrorCode(-1001, 404);
ErrorCode.BAD_REQUEST             = new ErrorCode(-1010, 404);

I wanted to implement a similar pattern as what we do with Java enums. This enables me to use a constructor to pass values. The constructor then freezes the ErrorCode object - nice and convenient.

Usage: first import your enum class...

import {ErrorCode} from "../common/services/errors/ErrorCode";

Now, after importing the enum class, access it like so:

if( errCode.includes(ErrorCode.BAD_REQUEST.apiCode) ){...}

PS> This is used in conjunction with a Webpack setup using Babel to convert our ES6 classes down for browser compatibility.