// 例6

​

getUserId()

    .then(getUserMobileById)

    .then(function (mobile) {

        console.log('do sth with mobile:', mobile);

    }, function (error) {

        // getUserId 或者 getUerMobileById 时出现的错误

        console.error('error msg:' + error);

    });

​

function getUserId() {

    return new Promise(function (resolve, reject) {

        window.setTimeout(function () {

            if (Math.random() >= 0.5) {

                resolve(9876);

            } else {

                reject('not login user');

            }

        });

    });

}

​

function getUserMobileById(id) {

    return new Promise(function (resolve, reject) {

        console.log('start to get user mobile by id:', id);

        window.setTimeout(function () {

            if (Math.random() >= 0.5) {

                resolve(13810001000);

            } else {

                reject('no mobile related to this user');

            }

        });

    });

}

​

function Promise(fn) {

    var state = 'pending',

        value = null,

        deferreds = [];

    this.then = function (onFulfilled, onRejected) {

        return new Promise(function (resolve, reject) {

            handle({

                onFulfilled: onFulfilled || null,

                onRejected: onRejected || null,

                resolve: resolve,

                reject: reject

            });

        });

    };

​

    function handle(deferred) {

        if (state === 'pending') {

            deferreds.push(deferred);

            return;

        }

        var cb = state === 'fulfilled' ? deferred.onFulfilled : deferred.onRejected,

            ret;

        if (cb === null) {

            cb = state === 'fulfilled' ? deferred.resolve : deferred.reject;

            cb(value);

            return;

        }

        ret = cb(value);

        deferred.resolve(ret);

    }

​

    function resolve(newValue) {

        if (newValue && (typeof newValue === 'object' || typeof newValue === 'function')) {

            var then = newValue.then;

            if (typeof then === 'function') {

                then.call(newValue, resolve, reject);

                return;

            }

        }

        state = 'fulfilled';

        value = newValue;

        finale();

    }

​

    function reject(reason) {

        state = 'rejected';

        value = reason;

        finale();

    }

​

    function finale() {

        setTimeout(function () {

            deferreds.forEach(function (deferred) {

                handle(deferred);

            });

        }, 0);

    }

​

    fn(resolve, reject);

}