ES6箭头功能正在改变Meteor.publish中的范围 [英] ES6 Arrow function is changing the scope of this in Meteor.publish

问题描述

所以我开始在 Meteor 中使用ES6，但显然如果你尝试使用 Meteor.publish 语法一个箭头函数 this.userId 是未定义的，而如果您使用常规的函数（）{} this.userId 完美地工作，Im假设是一种透明过程，它将不同的指派给 userId ，但只是一个猜测，有没有人知道真正发生了什么？

So I been started using ES6 in Meteor, but apparently if you try to use Meteor.publish syntax with an arrow function, this.userId is undefined, while if you use it with a regular function(){} this.userId works perfectly, Im assuming is a kind of transpiler process that assign a different this, to userId but is just a guess, does anyone knows what really is happening?

Meteor.startup(function() {
    Meteor.publish("Activities", function() { //with function
        console.log(this.userId); //TS8vTE3z56LLcaCb5
    });
});

Meteor.startup(function() {
    Meteor.publish("Activities", ()=> { //with arrow function
        console.log(this.userId); //undefined
    });
});

推荐答案

这不是一个透视错误，箭头功能的href =https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions#Lexical_this功能。箭头函数自动将函数体的上下文设置为此处创建的上下文，在这种情况下，回调到 Meteor.publish 。这样可以防止Meteor重新绑定您的监听器功能的上下文。

This isn't a transpilation error, it's a feature of arrow functions. The arrow function automatically sets the context of the function body to the contexts here it was created, in this case the callback to Meteor.publish. This prevents Meteor from rebinding the context of your listener function.

从Meteor 发布文档：

在函数内部，这是发布处理程序对象

Inside the function, this is the publish handler object

如果您希望事情正常工作，您将需要使用旧校功能语法来允许Meteor正确设置上下文。

If you want things to work properly you will need to use the "old-school" function syntax to allow Meteor to set the context properly.

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