22 lines
517 B
JavaScript
22 lines
517 B
JavaScript
// @flow
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// Feature check:
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// The predicate function is defined after the conditional check
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function foo(x: string | Array<string>): string {
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if (is_string(x)) {
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// The use of `is_string` as a conditional check
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// should guarantee the narrowing of the type of `x`
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// to string.
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return x;
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} else {
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// Accordingly the negation of the above check
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// guarantees that `x` here is an Array<string>
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return x.join();
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}
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}
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function is_string(x): %checks {
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return typeof x === "string";
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}
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