Can we determine if the variable str is present in the set of values defined by Name?
Is it doable?
/* hypothetical code */
type Name = 'a1' | 'a2' | .... | 'z100';
function isName(str: string): str is Name {
switch (str) {
case 'a1':
case 'a2':
// ...
case 'z100':
return true;
default:
return false;
}
}
isName('alice') // -> true or false
Switching from a type to a runtime check is not possible. Types are removed during compile time, making it impossible to access any information from them at runtime. However, the opposite direction is feasible; you can convert a value into a type:
const Name = ['a1', 'a2', 'z100'] as const // array with all values
type Name = typeof Name[number]; // retrieve the same type as previously
function isName(str: string): str is Name {
return Name.indexOf(str as any) !== -1; // basic verification
}
isName('alice') // -> true or false
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