I need create named constant.
for example:
NAME_FIELD: {
CAR : "car",
COLOR: "color"}
using:
var temp = NAME_FIELD.CAR // valid
var temp2 = NAME_FIELD.CAR2 // throw exception
most of all I need to make this enum caused error if the key is not valid
most of all I need to make this enum caused error if the key is not valid
Unfortunately, you can't. The way you're doing pseudo-enums is the usual way, which is to create properties on an object, but you can't get the JavaScript engine to throw an error if you try to retrieve a property from the object that doesn't exist. Instead, the engine will return undefined.
You could do this by using a function, which obviously has utility issues.
Alternately (and I really don't like this idea), you could do something like this:
var NAME_FIELD$CAR = "car";
var NAME_FIELD$COLOR = "color";
Since you would access those as free identifiers, trying to read a value that didn't exist:
var temp2 = NAME_FIELD$CAR2;
...fails with a ReferenceError. (This is true even in non-strict mode code; the Horror of Implicit Globals only applies to writing to a free identifier, not reading from one.)
Now that custom setters and getters in plain javascript objects are deprecated, a solution could be to define a class for your object and a set function :
NAME_FIELD= {
CAR : "CAR",
COLOR: "COLOR"
};
function MyClass(){
}
MyClass.prototype.setProp = function (val) {
if (!(val in NAME_FIELD)) throw {noGood:val};
this.prop = val;
}
var obj = new MyClass();
obj.setProp(NAME_FIELD.CAR); // no exception
obj.setProp('bip'); // throws an exception
But as enums aren't a native construct, I'm not sure I would use such a thing. This smells too much as "trying to force a java feature in javascript". You probably don't need this.
