Generics

  1. 泛型

function identity<U>(arg: U): U {
    return arg;
}

let output = identity("myString");
  1. 限制 T extends

function merge<T extends object, U extends object>(objA: T, objB: U) {
    return Object.assign(objA, objB);
}

const mergedObj = merge({ name: 'Max', hobbies: ['Sports'] }, { age: 30 });
console.log(mergedObj);


interface Lengthy {
  length: number;
}

function countAndDescribe<T extends Lengthy>(element: T): [T, string] {
  let descriptionText = 'Got no value.';
  if (element.length === 1) {
    descriptionText = 'Got 1 element.';
  } else if (element.length > 1) {
    descriptionText = 'Got ' + element.length + ' elements.';
  }
  return [element, descriptionText];
}

console.log(countAndDescribe(['Sports', 'Cooking']));
  1. Object keyof
function extractAndConvert<T extends object, U extends keyof T>(obj: T, key: U) {
  return 'Value: ' + obj[key];
}

extractAndConvert({ name: 'Max' }, 'name');
  1. Class

class DataStorage<T extends string | number | boolean> {
  private data: T[] = [];

  addItem(item: T) {
    this.data.push(item);
  }

  removeItem(item: T) {
    if (this.data.indexOf(item) === -1) {
      return;
    }
    this.data.splice(this.data.indexOf(item), 1); // -1
  }

  getItems() {
    return [...this.data];
  }
}

const textStorage = new DataStorage<string>();
textStorage.addItem('Max');
textStorage.addItem('Manu');
textStorage.removeItem('Max');
console.log(textStorage.getItems());

const numberStorage = new DataStorage<number>();