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 http://stackoverflow.com/questions/287903/enums-in-javascript — Travesty3, Feb 03 '12 at 13:26

score 7 · Accepted Answer · edited Nov 12 '12 at 20:30

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 '12 at 20:30

Community

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answered Feb 03 '12 at 13:25

dougajmcdonald

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Thanks. You are capitalizing the object name here because it refers to a constructor function (Object)? – Ben Aston Feb 03 '12 at 13:31
Not particularly, just a hark back to C# and the way we'd use upper case in there. – dougajmcdonald Feb 03 '12 at 13:35

score 1 · Answer 2 · answered Feb 03 '12 at 13:29

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 03 '12 at 13:29

Sirko

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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 Jan 14 '22 at 09:14
Better starting the above with `const value = (function...` I think. – aamarks Jan 14 '22 at 09:20
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`const` wouldnt help you with that. You would need to use something like [`Object.freeze()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze) if you want to account for this case. – Sirko Jan 14 '22 at 10:05

score 0 · Answer 3 · edited Jul 18 '13 at 09:57

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 '13 at 09:57

Umber Ferrule

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answered Feb 03 '12 at 13:25

Jamie Dixon

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

3 Answers3