44 lines
1.8 KiB
TypeScript
44 lines
1.8 KiB
TypeScript
// In the right operand of a && operation,
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// the type of a variable or parameter is narrowed by any type guard in the left operand when true.
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function foo(x: number | string) {
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return typeof x === "string" && x.length === 10; // string
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}
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function foo2(x: number | string) {
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// modify x in right hand operand
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return typeof x === "string" && ((x = 10) && x); // string | number
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}
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function foo3(x: number | string) {
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// modify x in right hand operand with string type itself
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return typeof x === "string" && ((x = "hello") && x); // string | number
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}
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function foo4(x: number | string | boolean) {
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return typeof x !== "string" // string | number | boolean
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&& typeof x !== "number" // number | boolean
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&& x; // boolean
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}
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function foo5(x: number | string | boolean) {
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// usage of x or assignment to separate variable shouldn't cause narrowing of type to stop
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var b: number | boolean;
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return typeof x !== "string" // string | number | boolean
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&& ((b = x) && (typeof x !== "number" // number | boolean
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&& x)); // boolean
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}
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function foo6(x: number | string | boolean) {
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// Mixing typeguard narrowing in if statement with conditional expression typeguard
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return typeof x !== "string" // string | number | boolean
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&& (typeof x !== "number" // number | boolean
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? x // boolean
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: x === 10) // number
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}
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function foo7(x: number | string | boolean) {
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var y: number| boolean | string;
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var z: number| boolean | string;
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// Mixing typeguard narrowing
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return typeof x !== "string"
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&& ((z = x) // number | boolean
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&& (typeof x === "number"
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// change value of x
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? ((x = 10) && x.toString()) // x is number
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// do not change value
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: ((y = x) && x.toString()))); // x is boolean
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}
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