Is there a method to refine a string to match an enum key in TypeScript without needing to re-cast it?
enum SupportedShapes {
circle = 'circle',
triangle = 'triangle',
square = 'square',
}
declare const square: string;
if (square in SupportedShapes) { // Any way to make this check refine `square`?
SupportedShapes[square]; // Err. "square as SupportedShapes" works here, but trying to avoid that
}
To accomplish this task, you can utilize type predicates.
The concept involves defining a function that yields a boolean. This boolean denotes the outcome of the key is SupportedShapes expression, and you must provide the implementation:
enum SupportedShapes {
circle = 'circle',
triangle = 'triangle',
square = 'square',
}
declare const square: string;
if (isKeyOfSupportedShapes(square)) {
SupportedShapes[square];
}
function isKeyOfSupportedShapes(key: string): key is SupportedShapes {
return Object.prototype.hasOwnProperty.call(SupportedShapes, key);
}
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