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//// [typeGuardsInRightOperandOfOrOrOperator.ts]
// In the right operand of a || operation,
// the type of a variable or parameter is narrowed by any type guard in the left operand when false,
// provided the right operand contains no assignments to the variable or parameter.
function foo(x: number | string) {
return typeof x !== "string" || x.length === 10; // string
}
function foo2(x: number | string) {
// modify x in right hand operand
return typeof x !== "string" || ((x = 10) || x); // string | number
}
function foo3(x: number | string) {
// modify x in right hand operand with string type itself
return typeof x !== "string" || ((x = "hello") || x); // string | number
}
function foo4(x: number | string | boolean) {
return typeof x === "string" // string | number | boolean
|| typeof x === "number" // number | boolean
|| x; // boolean
}
function foo5(x: number | string | boolean) {
// usage of x or assignment to separate variable shouldn't cause narrowing of type to stop
var b: number | boolean;
return typeof x === "string" // string | number | boolean
|| ((b = x) || (typeof x === "number" // number | boolean
|| x)); // boolean
}
function foo6(x: number | string | boolean) {
// Mixing typeguard
return typeof x === "string" // string | number | boolean
|| (typeof x !== "number" // number | boolean
? x // boolean
: x === 10) // number
}
function foo7(x: number | string | boolean) {
var y: number| boolean | string;
var z: number| boolean | string;
// Mixing typeguard narrowing
return typeof x === "string"
|| ((z = x) // number | boolean
|| (typeof x === "number"
// change value of x
? ((x = 10) && x.toString()) // number | boolean | string
// do not change value
: ((y = x) && x.toString()))); // number | boolean | string
}
//// [typeGuardsInRightOperandOfOrOrOperator.js]
// In the right operand of a || operation,
// the type of a variable or parameter is narrowed by any type guard in the left operand when false,
// provided the right operand contains no assignments to the variable or parameter.
function foo(x) {
return typeof x !== "string" || x.length === 10; // string
}
function foo2(x) {
// modify x in right hand operand
return typeof x !== "string" || ((x = 10) || x); // string | number
}
function foo3(x) {
// modify x in right hand operand with string type itself
return typeof x !== "string" || ((x = "hello") || x); // string | number
}
function foo4(x) {
return typeof x === "string" // string | number | boolean
|| typeof x === "number" // number | boolean
|| x; // boolean
}
function foo5(x) {
// usage of x or assignment to separate variable shouldn't cause narrowing of type to stop
var b;
return typeof x === "string" // string | number | boolean
|| ((b = x) || (typeof x === "number" // number | boolean
|| x)); // boolean
}
function foo6(x) {
// Mixing typeguard
return typeof x === "string" // string | number | boolean
|| (typeof x !== "number" // number | boolean
? x // boolean
: x === 10); // number
}
function foo7(x) {
var y;
var z;
// Mixing typeguard narrowing
return typeof x === "string"
|| ((z = x) // number | boolean
|| (typeof x === "number"
// change value of x
? ((x = 10) && x.toString()) // number | boolean | string
// do not change value
: ((y = x) && x.toString()))); // number | boolean | string
}
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