Introduction to Proxy and Reflect in ES6 (code example)

This article brings you an introduction to Proxy and Reflect in ES6 (code examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Proxy agent

{
    // 原始对象，或者真实数据，可以理解为供应商
    let obj = {
        time: '2018-10-05',
        name: 'lucy',
        age: 16,
        _is: true
    };

    // 代理对象，可以理解为代理商，对用户来说，直接操作monitor，而不能直接操作obj
    let monitor = new Proxy(obj, {
        // 拦截对象属性的读取
        get(target, key) {
            return target[key].replace('2018', '2019');
        },
        // 拦截对象设置属性
        set(target, key, value) {
            // 只让用户修改name属性，其他的不允许修改
            if (key === 'name') {
                return target[key] = value;
            } else {
                return target[key];
            }
        },
        // 拦截 key in object 操作
        has(target, key) {
            // 只暴露name属性，其他的都不暴露
            if (key === 'name') {
                return target[key];
            } else {
                return false;
            }
        },
        // 拦截delete
        deleteProperty(target, key) {
            // 属性名以_下划线开头的，就允许删除，否则不允许删除
            if (key.indexOf('_') > -1) {
                delete target[key];
                return true;
            } else {
                return target[key];
            }
        },
        // 拦截Object.keys Object.getOwnPropertySymbols, Object.getOwnPropertyNames
        ownKeys(target) {
            // 拦截了time属性
            return Object.keys(target).filter(item => item != 'time');
        }
    });
    console.log('get', monitor.time); // 2019-10-05
    monitor.time = '2020';
    monitor.name = 'can';
    console.log('set', monitor.time, monitor.name); // 2019-10-05 can
    console.log('has', 'name' in monitor, 'time' in monitor); // true false
    delete monitor.time;
    delete monitor._is;
    console.log(monitor); // Proxy {time: "2018-10-05", name: "can", age: 16}
    console.log('ownKeys', Object.keys(monitor)) // ["name", "age"]
}

Reflect reflection

Reflection is object, Reflect’s method is the same as Proxy’s, both have get ,set,has...

{
    let obj = {
        time: '2018-10-05',
        name: 'ahhh',
        age: 16,
        _is: true
    };
    console.log(Reflect.get(obj, 'time')); // 2018-10-05
    Reflect.set(obj, 'name', 'lxc');
    console.log(obj); // {time: "2018-10-05", name: "lxc", age: 16, _is: true}
    console.log(Reflect.has(obj, 'name')); // true
}

Data verification example

{
    function validator(target, validator) {
        return new Proxy(target, {
            _validator: validator,
            // 对set进行拦截
            set(target, key, value, proxy) {
                if (target.hasOwnProperty(key)) {
                    let va = this._validator[key]; // 拿到_validator配置好的方法
                    if (!!va(value)) {
                        // 允许修改
                        return Reflect.set(target, key, value, proxy);
                    } else {
                        // 抛出异常
                        throw Error(`不能设置${key}到${value}`);
                    }
                } else {
                    throw Error(`${key} 不存在`);
                }
            }
        });
    }

    const personValidators = {
        name(val) {
            // 如果name设置为字符串，则允许修改，否则抛出异常
            return typeof val === 'string';
        },
        age(val) {
            // 如果age设置为数值类型并且大于18，则允许修改，否则抛出异常
            return typeof val === 'number' && val > 18;
        }
    };

    class Person {
        constructor(name, age) {
            this.name = name;
            this.age = age;
            // 返回了一个Proxy对象，用户操作的并不是Person这个实例，而是这个实例的代理对象
            return validator(this, personValidators);
        }
    }

    const person = new Person('haha', 18);
    console.log(person); // Proxy {name: "haha", age: 18}

    // person.name = 46; // 不能设置name到46
    // person.age = 20; // 不能设置age到12
    // person.number = 111; // number 不存在

    person.name = 'yoyo';
    person.age = 20;
    console.log(person); // Proxy {name: "yoyo", age: 20}
}

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