197 lines
7.3 KiB
TypeScript
197 lines
7.3 KiB
TypeScript
//// [typeGuardsInConditionalExpression.ts]
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// In the true expression of a conditional expression,
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// the type of a variable or parameter is narrowed by any type guard in the condition when true,
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// provided the true expression contains no assignments to the variable or parameter.
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// In the false expression of a conditional expression,
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// the type of a variable or parameter is narrowed by any type guard in the condition when false,
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// provided the false expression contains no assignments to the variable or parameter.
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function foo(x: number | string) {
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return typeof x === "string"
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? x.length // string
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: x++; // number
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}
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function foo2(x: number | string) {
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// x is assigned in the if true branch, the type is not narrowed
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return typeof x === "string"
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? (x = 10 && x)// string | number
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: x; // string | number
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}
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function foo3(x: number | string) {
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// x is assigned in the if false branch, the type is not narrowed
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// even though assigned using same type as narrowed expression
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return typeof x === "string"
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? (x = "Hello" && x) // string | number
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: x; // string | number
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}
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function foo4(x: number | string) {
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// false branch updates the variable - so here it is not number
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// even though assigned using same type as narrowed expression
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return typeof x === "string"
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? x // string | number
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: (x = 10 && x); // string | number
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}
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function foo5(x: number | string) {
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// false branch updates the variable - so here it is not number
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return typeof x === "string"
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? x // string | number
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: (x = "hello" && x); // string | number
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}
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function foo6(x: number | string) {
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// Modify in both branches
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return typeof x === "string"
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? (x = 10 && x) // string | number
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: (x = "hello" && x); // string | number
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}
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function foo7(x: number | string | boolean) {
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return typeof x === "string"
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? x === "hello" // string
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: typeof x === "boolean"
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? x // boolean
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: x == 10; // number
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}
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function foo8(x: number | string | boolean) {
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var b: number | boolean;
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return typeof x === "string"
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? x === "hello"
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: ((b = x) && // number | boolean
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(typeof x === "boolean"
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? x // boolean
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: x == 10)); // number
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}
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function foo9(x: number | string) {
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var y = 10;
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// usage of x or assignment to separate variable shouldn't cause narrowing of type to stop
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return typeof x === "string"
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? ((y = x.length) && x === "hello") // string
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: x === 10; // number
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}
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function foo10(x: number | string | boolean) {
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// Mixing typeguards
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var b: boolean | number;
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return typeof x === "string"
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? x // string
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: ((b = x) // x is number | boolean
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&& typeof x === "number"
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&& x.toString()); // x is number
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}
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function foo11(x: number | string | boolean) {
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// Mixing typeguards
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// Assigning value to x deep inside another guard stops narrowing of type too
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var b: number | boolean | string;
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return typeof x === "string"
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? x // number | boolean | string - changed in the false branch
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: ((b = x) // x is number | boolean | string - because the assignment changed it
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&& typeof x === "number"
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&& (x = 10) // assignment to x
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&& x); // x is number | boolean | string
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}
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function foo12(x: number | string | boolean) {
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// Mixing typeguards
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// Assigning value to x in outer guard shouldn't stop narrowing in the inner expression
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var b: number | boolean | string;
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return typeof x === "string"
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? (x = 10 && x.toString().length) // number | boolean | string - changed here
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: ((b = x) // x is number | boolean | string - changed in true branch
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&& typeof x === "number"
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&& x); // x is number
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}
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//// [typeGuardsInConditionalExpression.js]
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// In the true expression of a conditional expression,
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// the type of a variable or parameter is narrowed by any type guard in the condition when true,
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// provided the true expression contains no assignments to the variable or parameter.
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// In the false expression of a conditional expression,
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// the type of a variable or parameter is narrowed by any type guard in the condition when false,
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// provided the false expression contains no assignments to the variable or parameter.
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function foo(x) {
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return typeof x === "string"
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? x.length // string
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: x++; // number
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}
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function foo2(x) {
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// x is assigned in the if true branch, the type is not narrowed
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return typeof x === "string"
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? (x = 10 && x) // string | number
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: x; // string | number
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}
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function foo3(x) {
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// x is assigned in the if false branch, the type is not narrowed
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// even though assigned using same type as narrowed expression
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return typeof x === "string"
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? (x = "Hello" && x) // string | number
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: x; // string | number
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}
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function foo4(x) {
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// false branch updates the variable - so here it is not number
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// even though assigned using same type as narrowed expression
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return typeof x === "string"
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? x // string | number
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: (x = 10 && x); // string | number
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}
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function foo5(x) {
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// false branch updates the variable - so here it is not number
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return typeof x === "string"
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? x // string | number
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: (x = "hello" && x); // string | number
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}
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function foo6(x) {
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// Modify in both branches
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return typeof x === "string"
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? (x = 10 && x) // string | number
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: (x = "hello" && x); // string | number
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}
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function foo7(x) {
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return typeof x === "string"
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? x === "hello" // string
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: typeof x === "boolean"
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? x // boolean
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: x == 10; // number
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}
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function foo8(x) {
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var b;
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return typeof x === "string"
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? x === "hello"
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: ((b = x) &&
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(typeof x === "boolean"
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? x // boolean
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: x == 10)); // number
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}
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function foo9(x) {
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var y = 10;
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// usage of x or assignment to separate variable shouldn't cause narrowing of type to stop
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return typeof x === "string"
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? ((y = x.length) && x === "hello") // string
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: x === 10; // number
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}
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function foo10(x) {
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// Mixing typeguards
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var b;
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return typeof x === "string"
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? x // string
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: ((b = x) // x is number | boolean
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&& typeof x === "number"
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&& x.toString()); // x is number
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}
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function foo11(x) {
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// Mixing typeguards
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// Assigning value to x deep inside another guard stops narrowing of type too
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var b;
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return typeof x === "string"
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? x // number | boolean | string - changed in the false branch
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: ((b = x) // x is number | boolean | string - because the assignment changed it
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&& typeof x === "number"
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&& (x = 10) // assignment to x
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&& x); // x is number | boolean | string
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}
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function foo12(x) {
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// Mixing typeguards
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// Assigning value to x in outer guard shouldn't stop narrowing in the inner expression
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var b;
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return typeof x === "string"
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? (x = 10 && x.toString().length) // number | boolean | string - changed here
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: ((b = x) // x is number | boolean | string - changed in true branch
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&& typeof x === "number"
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&& x); // x is number
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}
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