1.
Antifragile< >
Philipp Sapronov
philipp.sapronov@gmail.com

2.
Antifragility is a property of systems in
which they increase in capability to thrive as
a result of stressors, shocks, volatility, noise,
mistakes, faults, attacks, or failures.

3.
Developers

4.
Strict
Structural
Turing Complete
Type system is:

5.
Strict

6.
" ": ,
strict
// "noImplicitAny": true,
// "strictNullChecks": true,
// "strictFunctionTypes": true,
// "strictBindCallApply": true,
// "strictPropertyInitialization": true,
// "noImplicitThis": true,
// "alwaysStrict": true,
true
Strict

7.
A Note on Soundness
TypeScript’s type system allows certain operations that can’t be known at
compile-time to be safe. When a type system has this property, it is said to not be
“sound”. {...}
https://www.typescriptlang.org/docs/handbook/type-compatibility.html
Strict

8.
Strict
any
Strict

9.
unknown
ts before
try
catch
{}
( : ) {}
e any
ts v4.0+
try
catch
{}
( : ) {}
e unknown
Strict

10.
const : [] = []
[ ]. ()
arr
arr
string
0 split // error
Strict

11.
/* tsconfig.json */
// v4.1+
" ": ,
noUncheckedIndexedAccess true
Strict

12.
// "noUncheckedIndexedAccess": true,
// string | undefined
const : [] = []
[ ]
arr
arr
string
0
Strict

13.
A
B
|
Union
type T1 =
|
string
number
T1: string | number
type T2 =
|
{a: string}
{b: number}
T2: {a: string} | {b: number}
Strict

14.
interface
const
return
User
User
user
{
?: ;
}
= ( : ) => {
.email. ();
}
email string | null
getEmail
toLowerCase
user
Strict

15.
( .email ). ();
user as string toLowerCase
Strict

16.
Casting
( ).method()
null as any
A as
B
(( ...) ...)
null as as
Strict

17.
About narrowing (guards)
typescriptlang.org/docs/handbook/2/narrowing.html
Strict

18.
Strict
// typeof type guards
/*...*/
// instanceof narrowing
/*...*/
// The “in” operator narrowing
/*...*/
// Using type predicates
if
if instanceof
if in
function is
(typeof “ ”) { }
( ) { }
(“ ” ) { }
( : ):
str
x Date
x
Shape Circle
=== string
property
isCircle shape shape

19.
Structural

20.
interface
const
const =>
{
: ;
: ;
};
= : , : ;
= ( : ) {};
( );
( : , : );
Point
point: Point
fn point Point
fn point
fn
x
y
x y
x y
number
number
100 100
100 100
{ }
{ }
// OK
// OK
Structural

21.
const =>
const
= ( : : , : ) {};
= : , : ;
( );
fn point
point
fn point
{ }
{ }
x y
x y z
number number
1.5 2.4, : 999999
// OK
Structural

22.
const
const
: , : ;
. ( ). (( ) => {
= [ ];
});
point
point
value point
= x y
Object
{ }
1.5 2.4
keys forEach key
key
/**
* Element implicitly has an 'any' type because expression of type 'string'
* can't be used to index type '{ x: number; y: number; }'.
*/
Structural

23.
// lib.es5.d.ts
// proposal
< >
keys
keys
( : ): []
( : T): ( )[]
o
o
object string
object
T T
extends keyof
Structural

24.
type
function
for const of
if === === return
throw new
const
= : ; :
( : ) {
( . ) {
( " " || " ") ;
(" ");
}
}
= : , : ,
( );
Point
Point
key
key key
Error
point
point
{ }
{ }
x y
Object ( )
x y z
number number ;
x y
This is impossible
0.5 2.4 : 999999999
fn
keys
fn
point
point // (x | y)[]
// Throws an exception
https://stackoverflow.com/questions/55012174/why-doesnt-object-keys-return-a-keyof-type-in-typescript
Structural

25.
Branding and Type-Tagging
Structural

26.
const bar
bar bar bar bar bar
=
Object
{ }
foo “ ”
: ;
. ( , , , , )
bar
assign // any
Structural

27.
// lib.es5.d.ts
assign
assign
assign
assign
< , >( : , : ): & ;
< , , >( : , : , : ): & & ;
< , , , >( : , : , : , : ): & & & ;
( : , : []): ;
T U target source
T U V target source1 source2
T U V W target source1 source2 source3
target sources
T U T U
T U V T U V
T U V W T U V W
object ... any any
Structural

28.
A
B
&
Intersection
type T1 =
&
string
number
T1: never
type T2 =
&
{a: string}
{b: number}
T2: {a: string, b: number}
Structural

29.
// X | Y | Z => X & Y & Z
type =
extends ? => : extends =>
?
:
UnionToIntersection U
U : U : I
I
;
< >
infer
( k ) (k )
any void never void
never
( )
assign< , []>( : , : ):
& < [ ]>;
T P T P
T UnionToIntersection P
extends extends
object object
number
t sources
...
Structural

30.
TypeScript
Structural

31.
Turing Complete

32.
Generic Types
Conditional Types
Recursive Types
Mapped Types
Turing complete

33.
Cup<T>
Turing complete

34.
< > =
T *
type
Turing complete

35.
type < >
Identity T T
=
type < , > [ , ]
Pair T U T U
=
const =>
( )
identity t t
=
const =>
( , ) [ , ]
pair t u t u
=

36.
function
=>
const
< >
( : | (() )): [ , < < >>];
[ , ] < | >( )
( )
useState
Dispatch SetStateAction
state setState useState
setState
S
S S S S
initialState
null
= string null
/* only string or null is allowed */
Turing complete

37.
type
type extends
=>
const extends =>
return
{ : };
< > = {
: [];
: ( : ) ;
};
= < >( : < >) {
{ } ;
};
Row
TableProps T Row
T
T
T Row TableProps T
= id
rows
onClick void
string
row
props
Table
< > </ >
table table
/* ... */
Turing complete

38.
interface extends
const extends =>
const
return
< . < >> {
: ;
: < >;
}
= <T . < >>( : < >) {
{ : , } ;
{ } ;
};
Props T React ComponentType
T
React.ComponentProps T
React ComponentType Props T
component Component componentProps props
componentProps
any
component
componentProps
any
=
Item props
< />
Component ...
?
Turing complete

39.
Conditional types
Turing complete

40.
? :
===
typeof a “ ”
boolean true false
Turing complete

41.
? :
extends
A boolean true false
? :
===
typeof a “ ”
boolean true false

42.
*
? :
extends
A B *
Turing complete

43.
never
? :
extends
T U T
type Exclude<T, U> =
Exclude< | , >
'username' 'email' 'email' // username
Turing complete

44.
infer
Turing complete

45.
type extends ? :
type
type
< > < > ;
< []>;
<[ ]>;
ArrayType T T Array
T1 ArrayType
T2 ArrayType
= U U never
= string
= string, number
infer
// string
// string | number
Turing complete

46.
type extends ? :
type
< > < > < > ;
< < | < < < >>>>>;
ArrayType T T Array ArrayType
T2 ArrayType Array Array Array Array
= U U never
= string number
infer
// string | number
Turing complete
// v4.1+

47.
type
extends keyof
extends
?
: extends keyof
?
:
<
. | < >>
. < >
.
. [ ]
{};
ComponentProps
T JSX IntrinsicElements JSXElementConstructor
T React JSXElementConstructor
T JSX IntrinsicElements
JSX IntrinsicElements T
any =
P
P
infer
Turing complete

48.
interface extends
const extends =>
const
return
< . < >> {
: ;
: < >;
}
= <T . < >>( : < >) {
{ : , } ;
{ } ;
};
Props T React ComponentType
T
React.ComponentProps T
React ComponentType Props T
component Component componentProps props
componentProps
any
component
componentProps
any
=
Item props
< />
Component ...
Turing complete

49.
type keyof
type extends
type extends
Component JSX IntrinsicElements JSXElementConstructor
OptionalProps T T
Props T Component
T
React.ComponentProps T
OptionalProps T
= any
=
errorMessage
any
component
componentProps
. | < >
< > ‘ ’;
? { : }
: {};
< < >> {
: ;
: < >;
} & < >;
input
string
Turing complete

50.
Mapped types
Turing complete

51.
interface
const =>
const =>
const
{
: ;
: ;
: ;
}
( : ) { };
() {
[ , ] = < >( );
};
SignUpData
SignUpData
state setState useState SignUpData
email
password
username
=
=
string
string
string
// api/auth
/* ... */
// components/auth
signUp
SignUpForm
data
{}
Turing complete

52.
interface
const =>
const =>
const
{
: ;
: ;
: ;
}
( : ) { };
() {
[ , ] = < < >>( );
};
SignUpData
SignUpData
state setState useState Partial SignUpData
email
password
username
=
=
string
string
string
// api/auth
/* ... */
// components/auth
signUp
SignUpForm
data
{}
Turing complete

53.
{
}
email
password
username
:
, :
, :
string
string
string
{
}
email
password
username
?:
, ?:
, ?:
string
string
string
Turing complete

54.
{ }
[ ]
in :
K * *
Turing complete

55.
type Partial<T> =
{ }
[ ]
in ?:
K keyof T T[K]
Turing complete

56.
type Required<T> =
{ }
[ ]-
in ?:
K keyof T T[K]
Turing complete

57.
Exclude
Extract
Pick
Omit
Partial
ReturnType
Parameters
Challenge :)
Turing complete

58.
Links
www.typescriptlang.org
@why_typescript_is_bad
freecodecamp.org/news/typescript-curry-ramda-types-f747e99744ab
ybogomolov.me/typesafe-typescript
github.com/type-challenges/type-challenges
github.com/millsp/ts-toolbelt

59.
Thank s!