1{
2  using resource = getResource();
3	using reader = resource.getReader();
4  const { value, done } = reader.read();
5} // 블록을 벗어날 때 'reader' => 'resource' 순으로 자원 해제

1interface Context {
2    name: string;
3    metadata: Record;
4}
5
6function setMetadata(_target: any, context: Context) {
7    context.metadata[context.name] = true;
8}
9
10class SomeClass {
11    @setMetadata
12    foo = 123;
13
14    @setMetadata
15    accessor bar = "hello!";
16
17    @setMetadata
18    baz() { }
19}
20
21const ourMetadata = SomeClass[Symbol.metadata];
22
23console.log(JSON.stringify(ourMetadata));
24// { "bar": true, "baz": true, "foo": true }

1// before 5.2, ✅ Possible
2type Pair = [first: string, second: number];
3// before 5.2, ❌ has an error
4type Pair = [first: string, number];
5type Args = [first: string, ...string[]];
6
7// after 5.2, ✅ Possible
8type Pair = [first: string, number];
9type Args = [first: string, ...string[]];

1// ✅ Possible
2declare const arr: (string | number)[];
3arr.map((it /* string | number */) => console.log(it));
4
5// ✅ Possible
6declare const arr2: Array<string | number>;
7arr2.map((it /* string | number */) => console.log(it));
8
9// ❌ TypeScript Error
10declare const arr3: string[] | number[];
11arr3.map((it /* unknown */) => console.log(it)); // This expression is not callable.

1const arr = [2, 4, 6, 1, 3, 5];
2_.equal(arr.toSorted(), [1, 2, 3, 4, 5, 6]);
3_.equal(arr, [2, 4, 6, 1, 3, 5]);
4
5const arr2 = [1, 2, 3, 4];
6_.equal(arr2.toSpliced(1, 1, 5), [1, 5, 3, 4]);
7_.equal(arr2, [1, 2, 3, 4]);
8
9const arr3 = [1, 2, 3];
10_.equal(arr3.toReverse(), [3, 2, 1]);
11_.equal(arr3, [1, 2, 3]);
12
13const arr4 = [1, 2, 3, 4];
14_.equal(arr4.with(1, 5), [1, 5, 3, 4]);
15_.equal(arr4, [1, 2, 3, 4]);

1const myWeakMap = new WeakMap();
2
3const key = Symbol();
4const someObject = { /*...*/ };
5
6// Works! ✅
7myWeakMap.set(key, someObject);
8myWeakMap.has(key);