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kay-adamof
kay-adamof

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[TypeScript] Creating a literal type union from object values

#typescript

Let's say you have the following JavaScript object:

const test = { a: "hello", b: "world", c: 0 }
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And you want to create a literal type union using the values of this object, namely "hello", "world", and 0.

type TestValues = "hello" | "world" | 0
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The answer would be as follows:

const test = { a: "hello", b: "world", c: 0 } as const // <== !!! type TestValues = (typeof test)[keyof typeof test] // type TestValues = 0 | "hello" | "world"
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Make sure to include as const.

If you forget to add it, the resulting type union would be a union of string and number, rather than the exact literal values.

const test = { a: "hello", b: "world", c: 0 } type TestValues = (typeof test)[keyof typeof test] // type TestValues = string | number
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By the way, if you want to create a similar type based on the keys of the object instead of the values, you can do it like this:

const test = { a: "hello", b: "world", c: 0 } type TestKeys = keyof typeof test // type TestKeys = "a" | "b" | "c"
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