Javascript

1. 请优化这段代码 ，提高可读性

function async_add (m, n, callback) {
    setTimeout(callback.bind(null, m+n), 500);
}

async_add(1, 2, function (res) {
    console.log(res);
    async_add(res, 3, function (res) {
        console.log(res);
        async_add(res, 5, function (res) {
            console.log(res);
            async_add(res, 10, function (res) {
                console.log(res);
                async_add(res, 25, function (res) {
                    console.log(res);
                    async_add(res, 37, function (res) {
                        console.log(res);
                        async_add(res, 48, function (res) {
                             console.log(res);
                        })
                    })
                });
            });
        });
    });
});

2. 请给出这段代码 的运行结果，并解释为什么

class Animal {
    constructor(pos) {
        this.pos = pos;
    }
}

class Whale extends Animal {
constructor(pos) {
    super(pos + 1);
}
swim() {
    this.pos <<= 1;
    setTimeout(function timer() {
    this.pos <<= 1;
    this.pos < 8 && setTimeout(timer, 0);
    console.log(this.pos);
    }, 0);
    console.log(this.pos);
}
}

var pos = 1;
const whale = new Whale(pos);
whale.swim();

3. 请实现下段代码

/**
interface Array<T> {
    //flatMap :: (t -> [u]) -> [t] -> [u]
    flatMap<U>(f: (item: T) => U[]): U[];

}
*/

Array.prototype.flatMap = function (f) {
    // 实现这个函数，使得下面的测试用例能够正确输出
    throw new Error('Not implemented yet!')
    
}


/**
* 测试用例
*/

const arr1 = [1, 2, 3], arr2 = ['a', 'b', 'c']
const CartesianProduct = arr1.flatMap(x => arr2.flatMap(y => [[x, y]]))
//result => [[1, 'a'], [1, 'b'],  [1, 'c'],  [2, 'a'], [2, 'b'], [2, 'c'], [3, 'a'], [3, 'b'], [3, 'c']]


const flattenArray = [[1, 2, 3], [4, 5, 6], [7, 8, 9]].flatMap(x => x)
//result => [1, 2, 3, 4, 5, 6, 7, 8, 9]

html/css

请根据此效果图，兼容现代浏览器，尽可能还原。 (不限框架，工具，预编译语言)

兼容性要求：Chrome / Firefox / IE 11 / Edge

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