JavaScript idiom for limiting a string to a number of discrete values

Question

In C# I might use an enumeration.

In JavaScript, how can I limit a value to a set of discrete values idiomatically?

Possible duplicate of stackoverflow.com/questions/287903/enums-in-javascript — Travesty3
– Travesty3, Commented Feb 3, 2012 at 13:26

Community · Accepted Answer · 2012-11-12 20:30:45Z

7

We sometimes define a variable in a JS class 'Enumerations' along these lines:

var Sex = {
    Male: 1,
    Female: 2
};

And then reference it just like a C# enumeration.

edited Nov 12, 2012 at 20:30

CommunityBot

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answered Feb 3, 2012 at 13:25

dougajmcdonald

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2 Comments

Ben Aston Over a year ago

Thanks. You are capitalizing the object name here because it refers to a constructor function (Object)?

dougajmcdonald Over a year ago

Not particularly, just a hark back to C# and the way we'd use upper case in there.

Sirko · Accepted Answer · 2012-02-03 13:29:20Z

1

There is no enumeration type in JavaScript. You could, however, wrap an object with a getter and setter method around it like

var value = (function() {
   var val;
   return {
      'setVal': function( v ) {
                   if ( v in [ listOfEnums ] ) {
                       val = v;
                   } else {
                       throw 'value is not in enumeration';
                   }
                },
      'getVal': function() { return val; }
   };
 })();

answered Feb 3, 2012 at 13:29

Sirko

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3 Comments

aamarks Over a year ago

thanks +1, but if you do something stupid and call it incorrectly value.setVal = 'debug Hell' you end up replacing the function with the string and that's where you are! ...Working now.

aamarks Over a year ago

Better starting the above with const value = (function... I think.

Sirko Over a year ago

const wouldnt help you with that. You would need to use something like Object.freeze() if you want to account for this case.

Umber Ferrule · Accepted Answer · 2013-07-18 09:57:06Z

0

Basically, you can't.

Strong typing doesn't exist in JavaScript, so it's not possible to confine your input parameters to a specific type or set of values.

edited Jul 18, 2013 at 9:57

Umber Ferrule

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answered Feb 3, 2012 at 13:25

Jamie Dixon

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