A typesafe enum implementation for JavaScript

enumClass.js

class Enum {

  constructor(type) {
    Enum.initEnumType(type);
    this.type = type;
  }
	
  /**
  * Initate enum values ** Internal use only
  * Iterate through given values and intiate enum value object
  */
  initValues(values) {
    
    var type = this.type;
    for (let i = 1; i < values.length; i++) {
      
      // Shape of enum value object
      const enumObj = {
        strValue: values[i],
        intValue: i,
        type: type,
        toString: () => values[i]
      };
      
      // Assign enum value as string to `this`
      Object.defineProperty(this, values[i], {
        value: enumObj,
        writable: false
      })
      
      // Assign enum value as int to `this`
      Object.defineProperty(this, i, {
        value: enumObj,
        writable: false
      })
    };
    
    // Turn on immutable
    Object.freeze(this);
  }
	
  /**
  * Check if an enum value belong to this type
  * enumValue: an enum value object
  */
  has(enumValue) {
    return enumValue.type === this.type && enumValue.strValue in this;
  }
  
  /** 
  * @Override
  * Display enum as its type (string)
  */
  toString() {
  	return this.type;
  }
}

Enum.initEnumType = function(type) {

  if (window.__GLOBAL__ENUM__TYPES == undefined) {
    
    // Case 1. No enum has been initated yet
    // Initiate __GLOBAL__ENUM__TYPES and store enum types as string
    window.__GLOBAL__ENUM__TYPES = [type];
    
  } else if (window.__GLOBAL__ENUM__TYPES.indexOf(type) > -1) {
    
    // Case 2. Enum type has already existed
    // Throw error
    throw new Error(`Enum type "${type}" has already existed`);
    
  } else {
    
    // Case 3. __GLOBAL__ENUM__TYPES already existed and enum type has not existed
    // push new type to __GLOBAL__ENUM__TYPES
    window.__GLOBAL__ENUM__TYPES.push(type);
    
  }

}

Enum.init = function() {
  let rs = new Enum(arguments[0]);
  rs.initValues(arguments);
  return rs;
}

/**** Usage ****
* Enum.init(typeName, value1, value2, ..., valueN)
****************/

var Types = Enum.init('Types', 'Number', 'String', 'Boolean');
var isEnumValueAType = Types.has(Types.Number);

// More at https://jsfiddle.net/hieunc229/69o7mped/