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tests/cases/conformance/expressions/typeGuards/typeGuardsInIfStatement.ts(139,17): error TS2339: Property 'toString' does not exist on type 'never'.
==== tests/cases/conformance/expressions/typeGuards/typeGuardsInIfStatement.ts (1 errors) ====
// In the true branch statement of an 'if' statement,
// the type of a variable or parameter is narrowed by any type guard in the 'if' condition when true.
// In the false branch statement of an 'if' statement,
// the type of a variable or parameter is narrowed by any type guard in the 'if' condition when false.
function foo(x: number | string) {
if (typeof x === "string") {
return x.length; // string
}
else {
return x++; // number
}
}
function foo2(x: number | string) {
if (typeof x === "string") {
x = 10;
return x; // number
}
else {
return x; // number
}
}
function foo3(x: number | string) {
if (typeof x === "string") {
x = "Hello";
return x; // string
}
else {
return x; // number
}
}
function foo4(x: number | string) {
if (typeof x === "string") {
return x; // string
}
else {
x = 10;
return x; // number
}
}
function foo5(x: number | string) {
if (typeof x === "string") {
return x; // string
}
else {
x = "hello";
return x; // string
}
}
function foo6(x: number | string) {
if (typeof x === "string") {
x = 10;
return x; // number
}
else {
x = "hello";
return x; // string
}
}
function foo7(x: number | string | boolean) {
if (typeof x === "string") {
return x === "hello"; // string
}
else if (typeof x === "boolean") {
return x; // boolean
}
else {
return x == 10; // number
}
}
function foo8(x: number | string | boolean) {
if (typeof x === "string") {
return x === "hello"; // string
}
else {
var b: number | boolean = x; // number | boolean
if (typeof x === "boolean") {
return x; // boolean
}
else {
return x == 10; // number
}
}
}
function foo9(x: number | string) {
var y = 10;
if (typeof x === "string") {
// usage of x or assignment to separate variable shouldn't cause narrowing of type to stop
y = x.length;
return x === "hello"; // string
}
else {
return x == 10; // number
}
}
function foo10(x: number | string | boolean) {
// Mixing typeguard narrowing in if statement with conditional expression typeguard
if (typeof x === "string") {
return x === "hello"; // string
}
else {
var y: boolean | string;
var b = x; // number | boolean
return typeof x === "number"
? x === 10 // number
: x; // x should be boolean
}
}
function foo11(x: number | string | boolean) {
// Mixing typeguard narrowing in if statement with conditional expression typeguard
// Assigning value to x deep inside another guard stops narrowing of type too
if (typeof x === "string") {
return x; // string | number | boolean - x changed in else branch
}
else {
var y: number| boolean | string;
var b = x; // number | boolean | string - because below we are changing value of x in if statement
return 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
);
}
}
function foo12(x: number | string | boolean) {
// Mixing typeguard narrowing in if statement with conditional expression typeguard
// Assigning value to x in outer guard shouldn't stop narrowing in the inner expression
if (typeof x === "string") {
return x.toString(); // string | number | boolean - x changed in else branch
}
else {
x = 10;
var b = x; // number | boolean | string
return typeof x === "number"
? x.toString() // number
: x.toString(); // boolean | string
~~~~~~~~
!!! error TS2339: Property 'toString' does not exist on type 'never'.
}
}
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