js 程序

let arr = ["item1", "item2", "item3"];
      let result = arr.forEach((item) => (item = item + " is yours"));
      console.log(arr);
      let res = arr.map((item) => (item = item + " is yours"));
      //   forEach没有返回值，
      console.log(result);
      /**
       * map有返回值,且将结果赋值到新的数组中，并没有改变原数组结果
       * forEach/map遍历读取集合，操作item似乎不能改变原集合
       */
      console.log(res, arr);
      //   如果需要改变原数组，采用角标方式来实现
      arr.forEach(
        (item, index, arr) => (arr[index] = arr[index] + " is yours")
      );
      arr.map((item, index, arr) => (arr[index] = arr[index] + " or theirs?"));
      console.log(arr);
      //   如下循环方式实现改变数组值;
      for (let i = 0; i < arr.length; i++) {
        arr[i] = arr[i] + " is yours!";
      }
      console.log(arr);
      arr = ["item4", "item5", "item6"];
      //   利用map的返回值特性，以原数组为核心，拼接出需要的元素成为新数组
      res = arr.map((item) => `<li><a href="">${item}</a></li>`);
      console.log(res);
      res = res.join("");
      //   res = "<ul>" + res + "</ul>";
      console.log(res);
      document.body.firstElementChild.insertAdjacentHTML("beforeend", res);
      /**
       * 字面量简化
       * 1. 变量的值和名相同，只写变量名
       * 2. 方法简化参考匿名函数规则
       */
      let pname = "cellphone";
      let product = {
        pname: pname,
        show: function (pname) {
          return `Do you have a ${pname}?`;
        },
      };
      console.log(product.show(pname));
      pname = "laptop";
      product = {
        pname,
        show: (pname) => `Do you have a ${pname}?`,
      };
      console.log(product.show(pname));
      /**
       * 解构赋值
       * [] {}为模版标志
       * ...剩余参数
       */
      let [p1, p2, ...p3] = arr;
      console.log(p1, p2, p3);
      console.log(p1, p2, ...p3);
      [p1, p2, p3, p4 = "itemx"] = arr;
      //   一个元素前面加...，会分解开
      console.log(p1, p2, p3, ...p4);
      //   克隆对象
      let products = { name: "camera", price: 1000, storage: 100 };
      let { ...camera } = products;
      console.log(camera);
      console.log(camera.name);
      //   解构传参
      products = { name: "fridge", price: 2000, storage: 10 };
      let { ...fridge } = products;
      function show(products) {
        console.log(`${products.name}'s price is ${products.price}`);
      }
      show(fridge);
      show({ name: "computer", price: 3000 });

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