A
arktype•2mo ago
Stuart B

Is it possible to define a type that does this?

I'm trying to define a morph that turns the presence of a string key into true and the absence of the key results in false. In the below, I can't work out how to define myType to get the result I want, or if it's even possible? 
const firstObject={
    name:'Alan',
    approved:'yes' // Or any other valid string value
}

const secondObject={
    name:'Bill'
    // NOTE: the approved key does not exist
}

const myType=type({
    name:'string',
    approved: // What do I need here?
})


const parsedFirstObject=myType(firstObject)
// Should produce {name:'Alan',approved:true}

const parsedSecondObject=myType(secondObject)
// Should produce {name:'Bill',approved:false}
const firstObject={
    name:'Alan',
    approved:'yes' // Or any other valid string value
}

const secondObject={
    name:'Bill'
    // NOTE: the approved key does not exist
}

const myType=type({
    name:'string',
    approved: // What do I need here?
})


const parsedFirstObject=myType(firstObject)
// Should produce {name:'Alan',approved:true}

const parsedSecondObject=myType(secondObject)
// Should produce {name:'Bill',approved:false}
To deal with the possible absence of the 'approved' key, I've tried to add a default, but then I can't apply a morph to turn it into a Boolean. If I don't apply a default but make it optional, then it ignores the approved key for secondObject. Am I missing something or is this not possible?
3 Replies
TizzySaurus
TizzySaurus•2mo ago
I guess something like
const t = type({
     name: "string",
     "approved?": "string",
}).pipe((value, ctx) => {
    if ("approved" in value) {
        return {...value, approved: true };
    return {...value, approved: false};
});
const t = type({
     name: "string",
     "approved?": "string",
}).pipe((value, ctx) => {
    if ("approved" in value) {
        return {...value, approved: true };
    return {...value, approved: false};
});
should work (I can't remember if the params are value, ctx or ctx, value, so you might need to swap them)
Stuart B
Stuart BOP•2mo ago
Damn, that's so obvious, thanks! It didn't occur to me to .pipe the entire type like that. I was trying to apply the morph within the definition of the '"approved" key instead. Much simpler this way!
TizzySaurus
TizzySaurus•2mo ago
Fwiw, you can one-line the return too 
).pipe(value => ({...value, approved: "approved" in value}));
).pipe(value => ({...value, approved: "approved" in value}));

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