无法从Promise的then函数setState [英] Couldn't setState from the then function of the Promise

问题描述

我正在尝试使用 fetch 函数从承诺更新状态。

I'm trying to update the state from the promise which I received using the fetch function.

componentDidMount(){

fetch(url).then((responseText) => {

     var response = responseText.json();

     response.then(function(response){
         this.setState(response);
     });

  });
}

我收到的错误是 setState 不是函数

I was getting the error that the setState is not an function

然后，我尝试 bind（this）传递此值如下所示。

Then, I tried to bind(this) to pass the this value like below.

componentDidMount(){

fetch(url).then((responseText) => {

     var response = responseText.json();

     response.then(function(response){
         this.setState(response);
     });

  }).bind(this);
}

现在也不行。再次出现相同的错误。

It is not working now also. Same error again.

推荐答案

这是因为的范围 ，当你尝试使用 Function.prototype.bind 时，你会发现一些事情。你的错误是你没有一直绑定到最后一个匿名函数。您可能想要做的是一直使用箭头函数，如下所示：

This is because of the scoping of this, so you're on to something when you're trying to use Function.prototype.bind. Your mistake is that you don't bind all the way down to the last anonymous function. What you probably want to do is use arrow functions all the way, like this:

componentDidMount(){
    fetch(url)
        .then((responseText) => responseText.json())
        .then((response) => this.setState(response));
}

箭头函数始终保持的上下文。

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