为什么这段代码抱怨我的 function 不是 function

Question

The code shown below produces this error:

x.authenticate(...).allDomains(...).myDomains is not a function

There is an up arrow (^) under the 'm' in "myDomains". I don't recognize this as being any of the usual patterns for producing this error. Can someone please tell me how I can fix this problem? Thanks.

#!/usr/bin/node

const allDomainsURL = 'https://77.247.183.107/domain/List?
const myDomainsURL = 'https://77.247.183.107/domain/Info?ApiKey=testapi&Password=testpass&Domain=[{*domain*}]&ResponseFormat=JSON';
process.env['NODE_TLS_REJECT_UNAUTHORIZED'] = 0; // Fixes "unable to verify the first certificate" error.
const fetch = require('node-fetch');

var domains = function() {

    this.dataObj = {
        'account' : '123456',
        'password': 'secret',
        'scratch' : [],
        'access'  : false,
        'data'    : {}
    };

    this.authenticate = function(dataObj) {
        this.dataObj.access = true;
        console.log('authenticate done.');
        return this;
    }

    this.allDomains = async function(dataObj) {
        const response = await fetch(allDomainsURL);
        this.dataObj.scratch = await response.json();
        this.dataObj.scratch = this.dataObj.scratch.domain;
        return this;
    }

    this.myDomains = async function(dataObj) {
        return this;
    }
}

var x = new domains();
x.authenticate('123456', 'secret').allDomains().myDomains();

// Error: TypeError: x.authenticate(...).allDomains(...).myDomains is not a function

Answer 1

The problem is that allDomains is an async function. That means it returns a promise. So, when you try to do:

x.authenticate('123456', 'secret').allDomains().myDomains();

You're trying to call .myDomains() on a promise and that method does not exist on a promise.

Remember, an async function ALWAYS returns a promise. The value you return in an async function just becomes the resolved value of that promise.

---

FYI, it is not easy to support the chaining of asynchronous methods. I'd suggest a different design structure if that's what you're trying to do. In this case, you can do this:

await x.authenticate('123456', 'secret').allDomains();
await x.myDomains();

PS Your authenticate method is only designed to accept one argument and the code you show doesn't even use that argument, yet you are passing it two arguments in your example, so something is not correct there.