promise.resolve上的状态错误无效

Question

浏览器：IE

我有下面的代码，它会抛出无效的状态错误并在异常catch块中执行promise.reject。

无效状态异常不会一直抛出，为什么？

下面的globalToken是undefined和promise.resolve（globalToken）;间歇性地抛出无效状态错误。

如何确保，xhr请求始终通过，无论承诺解决或拒绝

Promise.prototype = {
    then: function (resolveFn, rejectFn) {
        this._handler.push({resolve: resolveFn, reject: rejectFn});
    },
    resolve: function () {
        this._execute('resolve', arguments);
    },
    reject: function () {
        this._execute('reject', arguments);
    },
    _execute: function (result, args) {
        if (this._handler === null) {
            throw new Error('Promise already completed.');
        }

        for (var i = 0, ln = this._handler.length; i < ln; i++) {
            this._handler[i][result].apply(window, args);
        }

        this.then = function (resolveFn, rejectFn) {
            (result === 'resolve' ? resolveFn : rejectFn).apply(window, args);
        };

        this._handler = null;
    }

};

var promise, globalToken;

function getToken() {
    promise = new Promise();

    var xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function() {
        if (xhr.readyState === 4) {
            try {
                var data = JSON.parse(xhr.responseText);
                globalToken = data.token;
                promise.resolve(globalToken);
            } catch (ex) {
                promise.reject(xhr.responseText);
            }
        }
    };
    xhr.open('GET', Granite.HTTP.externalize(TOKEN_SERVLET), true);
    xhr.send();

    return promise;
}