遍历

   // 数组遍历方式

    let arr = ["a", "b"];

    //forEach
    arr.forEach((a, b) => {
        console.log(b, ":", a);
    })

    //for of
    for (const el of arr) {
        console.log(el, " indexof ", arr.indexOf(el));
    }


    // for in
    for (const key in arr) {
        if (Object.hasOwnProperty.call(arr, key)) {
            const element = arr[key];
            console.log(key, ":", element);
        }
    }

// 对象遍历方式

    // forin
    let arr = { name: "lisan", age: 24 };
    for (const key in arr) {
        console.log(key);
    }
    // keys方法
    Object.keys(arr).forEach(key => console.log("keys" + key));