1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
|
//// [typeGuardsInRightOperandOfAndAndOperator.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 true.
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 narrowing in if statement with conditional expression 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()) // x is number
// do not change value
: ((y = x) && x.toString()))); // x is boolean
}
//// [typeGuardsInRightOperandOfAndAndOperator.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 true.
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 narrowing in if statement with conditional expression 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()) // x is number
// do not change value
: ((y = x) && x.toString()))); // x is boolean
}
|
