Question

我对调用＆＃39;这个＆＃39;时得到的结果感到有点困惑。对象构造函数内部的变量。

function Slider(tag){
    this.tag = document.querySelector(tag),
    this.start = function(){
        return this.interval;
    },
    this.interval = setInterval(function(){
        console.log(this.tag); //undefined
        console.log(this); //window object
    }, 2000)
}
var route ={
    init:function(){        
        mySlide = new Slider('slider');
        mySlide.start();
    }
}
document.addEventListener('DOMContentLoaded', route.init);

我记录了标记console.log(this.tag)，但它返回undefined，并且在this内记录console.log(this)变量时，它引用了窗口对象。

Here is a Demo

问题：为什么没有console.log(this.tag)返回所选元素？

Answer 1

setInterval中匿名函数的范围是Window。如果你想让它成为Slider实例，你应该先bind它。

function Slider(tag){
this.tag = document.querySelector(tag),
this.start = function(){
    return this.interval;
},
this.interval = setInterval(function(){
    console.log(this.tag); //undefined
    console.log(this); //window object
}.bind(this), 2000)
}

Answer 2

这是因为当您将回调函数传递给def generate_random_hyperparams(lr_min, lr_max, kp_min, kp_max): '''generate random learning rate and keep probability''' # random search through log space for learning rate random_learng_rate = 10**np.random.uniform(lr_min, lr_max) random_keep_prob = np.random.uniform(kp_min, kp_max) return random_learning_rate, random_keep_prob时，它会在全局范围内调用。这就是为什么run_model是def run_model(random_learning_rate,random_keep_prob): # Note that the arguments is named differently from the placeholders in the graph graph = tf.Graph() with graph.as_default(): # graph here... learning_rate = tf.placeholder(tf.float32, name='learning_rate') keep_prob = tf.placeholder(tf.float32, name='keep_prob') # other operation ... with tf.Session(graph=graph) as session: tf.initialize_all_variables().run() # session here... feed_train = {data: batch_data, #placeholder variable names as dict key, python value variables as dict value learning_rate: random_learning_rate, keep_prob : random_keep_prob } # evaluate performance with random_learning_rate and random_keep_prob performance = session.run([...], feed_dict = feed_train) return performance。

您可以使用Function.bind()为performance_records = {} for i in range(10): # random search hyper-parameter space 10 times random_learning_rate, random_keep_prob = generate_random_hyperparams(-5, -1, 0.2, 0.8) performance = run_model(random_learning_rate, random_keep_prob) performance_records[(random_learning_rate, random_keep_prob)] = performance对象设置函数的上下文，并使其按您的意愿运行。

setInterval

另外，我只想指出this什么都不做。当你拨打window时，就是你的间隔时间。您的this只返回intervalID（仅用于this.interval = setInterval(function(){ console.log(this.tag); }.bind(this), 2000);）。实际上，因为你甚至没有使用mySlide.start();的返回值，所以调用它是没用的。

更新：另一种解决方案是在构造函数中使用new Slider('slider')，然后在mySlide.start();内使用clearInterval()：

mySlide.start();

更新：如果您使用的是支持"arrow functions"的浏览器，则可以执行以下操作：

var self = this;

使用＆＃39;这个＆＃39;对象构造函数

2 个答案: