Question

我有以下服务：

function Configuration($http, $q) {
    this.$http = $http;
    this.$q = $q;

    this.promises = [];

    this.getEnv().then(function(d) {
        this.env = d;
    });
}

Configuration.prototype.getEnv = function() {

    // only go get the environment setting if we don't already have it

    var deferred = this.$q.defer();

    if (this.promises.length > 0) {

        console.log('%cAdd to queue', 'color:orange;');
        this.promises.push(deferred);

    } else if (!this.env) {
        this.promises.push(deferred);
        console.log('%cFetch from live', 'color:red');

        // $http returns a promise, which has a then function, which also returns a promise
        var promise = this.$http.get('config/env.json').then(function(response) {
            // The then function here is an opportunity to modify the response
            console.log("environment variable is " + response.data.current_environment);
            // The return value gets picked up by the then in the controller.
            this.env = response.data.current_environment;

            var i;
            for (i = this.promises.length; i--;) {
                console.log('%cYay! Resolving the existing promises with a single server side request', 'color:white;background:deepskyblue');
                this.promises.shift().resolve(this.env);
            }
        });
    } else {
        console.log('%cFetch direct from this.env', 'color:green');
        deferred.resolve(this.env);
    }

    // Return the promise to the controller
    return deferred.promise;
};

我正在调试我正在构建的promises缓存，以防止多次点击服务器。不幸的是，Chrome中的JS引擎比Apache快得多。这个概念很简单，基本上是在缓存中记录promises，如果方法被命中，如果缓存中没有promise，运行它，如果缓存中有promises，那么就不执行它。

我的问题出现在for (i = this.promises.length; i--;) {会发生什么是this.promises未定义。我假设它，因为它在嵌套函数内部及其正常的JS变量范围不允许它访问父函数中的变量。但我不确定。

我有办法让这项工作成功吗？

Answer 1

您可以在this承诺回调之外缓存$http，因为在回调中您不再处于服务实例的上下文中： -

    var _this = this; //<-- Here

    var promise = this.$http.get('config/env.json').then(function(response) {


        _this.env = response.data.current_environment;

        var i;
        for (i = _this.promises.length; i--;) {

            _this.promises.shift().resolve(_this.env);
        }
    });

或者将服务实例的上下文绑定到回调。

   this.$http.get('config/env.json').then((function(response) {
        // The then function here is an opportunity to modify the response
        console.log("environment variable is " + response.data.current_environment);
        // The return value gets picked up by the then in the controller.
        this.env = response.data.current_environment;

        var i;
        for (i = this.promises.length; i--;) {
            console.log('%cYay! Resolving the existing promises with a single server side request', 'color:white;background:deepskyblue');
            this.promises.shift().resolve(this.env);
        }
    }).bind(this))

访问服务函数中子函数内的变量

1 个答案: