generate constants data structure from String of keys





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6yrs ago







Type Definitions






Create const/enum/bitmap object with key names specified in String, Array, Object or Arguments


npm install constjs

Enum (Java style)

var ConstJs = require('constjs');

var Colors = ConstJs.enum("blue red");

var myColor =;

console.log(myColor.isBlue()); // output true
console.log('blue')); // output true
console.log('BLUE')); // output true
console.log(; // output true
console.log(; // output true

console.log(myColor.isRed()); // output false
console.log('red')); // output false

console.log(myColor._id); // output blue
console.log(; // output blue
console.log(myColor.toString()); // output blue

// See how CamelCase is used to generate the isXxx() functions
var AppMode = ConstJs.enum('SIGN_UP, LOG_IN, FORGOT_PASSWORD');
var curMode = AppMode.LOG_IN;

console.log(curMode.isLogIn()); // output true
console.log(curMode.isSignUp()); // output false
console.log(curMode.isForgotPassword()); // output false

Enum serialization/deserialization with JSON

Adding methods to enum elements could be very handy for use, however there is major concern about applying this style. Once you serialize your enum into JSON format string and parse it back, you loose all methods and suddenly all your code doesn't work anymore. Fortunately constjs provides a way unJSON() to to help you alleviate this concern:

var ConstJs = require('constjs');


var Colors = ConstJs.enum('Red, Green, Blue');

var myData = {
    name: 'blah blah',
    color: Colors.Red
console.log(myData.color.isRed()); // output: true

var myDataStr = JSON.stringfy(myData);

myData = JSON.parse(myDataStr);
// console.log(myData.color.isRed()); // exception thrown out here
myData = ConstJs.unJSON(myData); 
// or myData = ConstJs.unJSON(JSON.parse(myDataStr)); the same effects
console.log(myData.color.isRed()); // output: true

However there is cost associated with the unJSON feature, say, your JSON string will contains additional data to support deserialization. If you are sure you don't need to deserialize your enum data, constjs provides a way to generate relatively more lightweight enum data.

Instead of

var Colors = ConstJs.enum('Red, Green, Blue');

You use enum.transient:

var Colors = ConstJs.enum.transient('Red, Green, Blue');

or use the alias enum.lite:

var Colors = ConstJs.enum.lite('Red, Green, Blue');

To compare the data been generated:

var Colors = ConstJs.enum('Red, Green, Blue');
var LiteColors = ConstJs.enum.lite('Red, Green, Blue');

var myColor = Colors.Red, myLiteColor = LiteColors.Red;
console.log({myColor: myColor, myLiteColor: myLiteColor});

You should be able to see something like:

    myColor: {_id: 'Red', _seq: 0, _kl: ['Red', 'Green', 'Blue']},
    myLiteColor: {_id: 'Red', _seq: 0}

And after unJSON call on myLiteColor, you will find that the isRed(), isGreen() and isBlue() method is no longer there. However you can still use name(), toString() and is() method on the myColor object after unJSON():

var s = JSON.stringify(myLiteColor);
var c = ConstJs.unJSON(s);

console.log(c.isRed); // output: undefined
console.log(; // output: 'Red'
console.log('Red')); // output: true

String Constants

var ConstJs = require('constjs');

var Weekdays = ConstJs.const("Mon, Tue, Wed");
console.log(Weekdays); // output {Mon: 'Mon', Tue: 'Tue', Wed: 'Wed'}

var today = Weekdays.Wed;
console.log(today); // output: 'Wed';


var ConstJs = require('constjs');

var ColorFlags = ConstJs.bitmap("blue red");
console.log(; // output false

var StyleFlags = ConstJs.bitmap(true, "rustic model minimalist");
console.log(StyleFlags.rustic); // output true

var CityFlags = ConstJs.bitmap({Chengdu: true, Sydney: false});
console.log(CityFlags.Chengdu); //output true
console.log(CityFlags.Sydney); // output false

var DayFlags = ConstJs.bitmap(true, {Mon: false, Tue: true});
console.log(DayFlags.Mon); // output false. Default val wont override specified val if the type is boolean 

Input variations

Instead of a string of keys sepated by separators specified above, it can use another two variaions of input to specify keys:

var ConstJs = require('constjs');

// use array of strings to specify keys
var Color = ConstJs.enum(["blue", "red"]);
var myColor =;

// use arguments array to specify keys
var BuildTool = ConstJs.enum("gulp", "grunt");
var myTool = BuildTool.gulp;

// use object to specify keys
var WeekDay = ConstJs.enum({
    Monday: null,
    Tuesday: null
var myDay = WeekDay.Monday;

The input variations are supported by all three generators: enum, const and bitmap


constjs tried to use Object.freeze() to make the enum/const object be immutabile:

var ConstJs = require('constjs');

// use array of strings to specify keys
var Color = ConstJs.enum(["blue", "red"]); = 'blue';
console.log(; // output {_id: 'blue', ...}

var WeekDay = ConstJs.const('Mon Tue');
WeekDay.Mon = false;
console.log(WeekDay.Mon); // output: 'Mon'
WeekDay.Wed = 'Wed';
console.log(WeekDay.Wed); // output: 'undefined'

For bitmap object, constjs use Object.seal() so the flag could be set/unset. However it still doesn't allow properties been removed or added:

var ConstJs = require('constjs');

var ColorFlags = ConstJs.bitmap("blue red"); = true;
console.log(; // output: true
ColorFlags.brown = false;
console.log(ColorFlags.brown); // output: 'undefined'

However constjs provided an immutable function to bitmap thus it ensure the data returned is completely frozen:

var ConstJs = require('constjs');

var ColorFlags = ConstJs.bitmap.immutable("blue red"); = true;
console.log(; // output: false
ColorFlags.brown = false;
console.log(ColorFlags.brown); // output: 'undefined'


  • lodash

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