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Compilation of discriminate unions to JavaScript
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Record types and discriminate unions are translated to JavaScript very differently:

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type Foobar = { Foo : int }
let foobar = { Foo = 42 }

gets translated into:

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foobar:Runtime.Field(function()
    {
     return{
      Foo:42
     };
    })

This seems correct and works.

On the other hand

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type Foobar = | Foo of int
let foobar = Foo 42

gets translated into:

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foobar:Runtime.Field(function()
    {
     return{
      $:0,
      $0:42
     };
    })

This seems a bit odd, and produces non-functional code in my real-life application (which is admittedly a bit more complicated). Adding [<NamedUnionCases>] does not produce a different result.

Perhaps I have misunderstood something, but is this correct? What is going on here?

.

As far as I know you cant really customize how DUs are represented in JavaScript. NamedUnionCasesAttribute on the type and NameAttribute only affect Json serializayion. That being said having the following type:

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[<NamedUnionCases "tag">]
type Foobar = | [<Name "foo">] Foo of value : int

maybe you could use Json.Encode: 'T -> obj on the values to get the right representation for values that you wish to expose. This is not the best solution obviously but this is the only thing that comes to mind which lets you customize how zour DUs look like. After encoding it the output would be something like:

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{
	tag: "foo",
    value: 42
}

as a JavaScript object.

By on 4/7/2016 4:20 PM ()

Thanks, this works and is a perfectly acceptable solution!

By on 4/9/2016 5:04 AM ()

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