什么是职责链模式

面向对象例子：

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export class Vip5{
    constructor() {
        this.level = 5;
    }

    getDiscount(pay, level) {
        if (level === this.level) {
            console.log(pay * 0.5);
        } else {
            this.nextChain.getDiscount(pay, level);
        }
    }

    setNextChain(obj) {
        this.nextChain = obj;
    }
}

export class Vip3{
    constructor() {
        this.level = 3;
    }

    getDiscount(pay, level) {
        if (level === this.level) {
            console.log(pay * 0.7);
        } else {
            this.nextChain.getDiscount(pay, level);
        }
    }

    setNextChain(obj) {
        this.nextChain = obj;
    }
}

export class Vip1{
    constructor() {
        this.level = 1;
    }

    getDiscount(pay, level) {
        if (level === this.level) {
            console.log(pay * 0.9);
        } else {
            this.nextChain.getDiscount(pay, level);
        }
    }

    setNextChain(obj) {
        this.nextChain = obj;
    }
}

函数式例子：

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(function () {

    var order = function (orderType, pay, stock) {
        if (orderType === 1) {
            if (pay === true) {
                console.log('500元定金预购，得到100优惠券');
            } else {
                if (stock > 0) {
                    console.log('普通购买');
                } else {
                    console.log('手机库存不足');
                }
            }
        } else if (ordertype === 2) {
            if (pay === true) {
                console.log('200元定金预购，得到50元优惠券');
            } else {
                if (stock > 0) {
                    console.log('普通购买');
                } else {
                    console.log('手机库存不足');
                }
            }
        } else if (orderType === 3) {
            if (stock > 0) {
                console.log('普通购买');
            } else {
                console.log('手机库存不足');
            }
        }
    }

    var Chain = function (fn) {
        this.fn = fn;
        this.successor = null;
    };

    Chain.prototype.setNextSuccessor = function (successor) {
        this.successor = successor;
    };

    Chain.prototype.passRequest = function () {
        var ret = this.fn.apply(this, arguments);
        if (ret === 'nextSuccessor') {
            return this.successor && this.successor.passRequest.apply(this.successor, arguments);
        }
    };

    var order500 = function (orderType, pay, stock) {
        if (orderType === 1 && pay === true) {
            console.log('500元定金预购，得到100元优惠券');
        } else {
            return 'nextSuccessor';
        }
    };

    var order200 = function (orderType, pay, stock) {
        if (orderType === 2 && pay === true) {
            console.log('200元定金预购，得到50元优惠券');
        } else {
            return 'nextSuccessor';
        }
    };

    var orderNormal = function (orderType, pay, stock) {
        if (stock > 0) {
            console.log('普通购买，无优惠券');
        } else {
            console.log('手机库存不足');
        }
    };

    var init = function () {
        order(1, true, 500);
        var chainOrder500 = new Chain(order500);
        var chainOrder200 = new Chain(order200);
        var chainOrderNomal = new Chain(orderNormal);

        chainOrder500.setNextSuccessor(chainOrder200);
        chainOrder200.setNextSuccessor(chainOrderNomal);
        chainOrder500.passRequest(1, false, 100);
    };
    init();
})();