//// [typeGuardsInIfStatement.ts] // 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, // provided the true branch statement contains no assignments to the variable or parameter. // 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, // provided the false branch statement contains no assignments to the variable or parameter function foo(x: number | string) { if (typeof x === "string") { return x.length; // string } else { return x++; // number } } function foo2(x: number | string) { // x is assigned in the if true branch, the type is not narrowed if (typeof x === "string") { x = 10; return x; // string | number } else { return x; // string | number } } function foo3(x: number | string) { // x is assigned in the if true branch, the type is not narrowed if (typeof x === "string") { x = "Hello"; // even though assigned using same type as narrowed expression return x; // string | number } else { return x; // string | number } } function foo4(x: number | string) { // false branch updates the variable - so here it is not number if (typeof x === "string") { return x; // string | number } else { x = 10; // even though assigned number - this should result in x to be string | number return x; // string | number } } function foo5(x: number | string) { // false branch updates the variable - so here it is not number if (typeof x === "string") { return x; // string | number } else { x = "hello"; return x; // string | number } } function foo6(x: number | string) { // Modify in both branches if (typeof x === "string") { x = 10; return x; // string | number } else { x = "hello"; return x; // string | number } } 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 } } //// [typeGuardsInIfStatement.js] // 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, // provided the true branch statement contains no assignments to the variable or parameter. // 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, // provided the false branch statement contains no assignments to the variable or parameter function foo(x) { if (typeof x === "string") { return x.length; // string } else { return x++; // number } } function foo2(x) { // x is assigned in the if true branch, the type is not narrowed if (typeof x === "string") { x = 10; return x; // string | number } else { return x; // string | number } } function foo3(x) { // x is assigned in the if true branch, the type is not narrowed if (typeof x === "string") { x = "Hello"; // even though assigned using same type as narrowed expression return x; // string | number } else { return x; // string | number } } function foo4(x) { // false branch updates the variable - so here it is not number if (typeof x === "string") { return x; // string | number } else { x = 10; // even though assigned number - this should result in x to be string | number return x; // string | number } } function foo5(x) { // false branch updates the variable - so here it is not number if (typeof x === "string") { return x; // string | number } else { x = "hello"; return x; // string | number } } function foo6(x) { // Modify in both branches if (typeof x === "string") { x = 10; return x; // string | number } else { x = "hello"; return x; // string | number } } function foo7(x) { if (typeof x === "string") { return x === "hello"; // string } else if (typeof x === "boolean") { return x; // boolean } else { return x == 10; // number } } function foo8(x) { if (typeof x === "string") { return x === "hello"; // string } else { var b = x; // number | boolean if (typeof x === "boolean") { return x; // boolean } else { return x == 10; // number } } } function foo9(x) { 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) { // Mixing typeguard narrowing in if statement with conditional expression typeguard if (typeof x === "string") { return x === "hello"; // string } else { var y; var b = x; // number | boolean return typeof x === "number" ? x === 10 // number : x; // x should be boolean } } function foo11(x) { // 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; 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) { // 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 } }