Call Class Function using string

Question

I want to call a NodeJS class using only a Class name and a method name. How do I do this if I only have the string value of the class and method? Assuming I have this controller

export default class PageController extends BaseController {
    async mainMethod(request, response) {
        const mapClass = {
            class: "MyClass",
           method: "testMethod",
        };

        global.${mapClass.class}.${mapClass.method}(); <-- How do I call the class MyClass.testMethod();
   }
}

Now in my MyClass.js I have this function

// Inside MyClass.js
export default class MyClass {
    testMethod(params) {
       return "My response here";
    }
}

UPDATE:

import resolver from '../services/Resolver';

export default class PageController extends BaseController {
    async mainMethod(request, response) {
        const mapClass = {
            class: "MyClass",
           method: "testMethod",
        };

       let classInstance = new resolver[mapClass.class];
       classInstance[mapClass.method]();
   }
}

// Inside ../services/Resolver.js

import MyClass from './MyClass';

export {
    MyClass,
}

// Content of MyClass.js
// Inside MyClass.js
export default class MyClass {
    testMethod(params) {
       return "My response here";
    }
}

Call just hangs when i reached the let classInstance = new resolver[mapClass.class]; and just gives me a request timeout

@Snow I'm just defining an object that contains the string value of the class and its method. And using that value I'm retrieving the class based from the string — MadzQuestioning
– MadzQuestioning, Commented May 9, 2019 at 7:13
@Seblor updated my question. I missed out the controller name — MadzQuestioning
– MadzQuestioning, Commented May 9, 2019 at 7:15
In your example MyClass is not a global. And it shouldn't be a global in modular envirionment. — Estus Flask
– Estus Flask, Commented May 9, 2019 at 7:17
Possible duplicate of How do I make JavaScript Object using a variable String to define the class name? — robe007
– robe007, Commented May 10, 2019 at 19:40

Mark · Accepted Answer · 2019-05-09 07:23:16Z

2

One way to do this is to create a lookup object so you can control what strings point to what classes rather than looking up things in some global space. Then you can grab the class object with a string key:

class MyClass {
    testMethod() {
       console.log("My response here");
    }
}

// create dispatch object mapping strings to classes
const classes = {MyClass}

class PageController  {
    mainMethod() {
        const mapClass = {
            class: "MyClass",
            method: "testMethod",
        };

        let instance = new classes[mapClass.class] // lookup class with string key
        instance[mapClass.method]()                // you can then lookup the method directly on the intance
   }
}

let p = new PageController()
p.mainMethod()

answered May 9, 2019 at 7:23

Mark

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5 Comments

MadzQuestioning Over a year ago

Hi @Mark Meyer I like your approach. But just a question what is const classes = {MyClass} do? I mean if I have 3 class should I write it something like this? const classes = {MyClass, MyClass2, MyClass3}

Mark Over a year ago

Yes, exactly. It will create an object with keys the same as the class names. It's also safer if the strings are coming from untrusted sources.

MadzQuestioning Over a year ago

Ok will try this and will accept your answer if this solves it

MadzQuestioning Over a year ago

Tried it and it didn't work. Not sure why but will update with what I have done

MadzQuestioning Over a year ago

Ok I tried it again and it worked but need to modify the let instance = new classes[mapClass.class] and added () to the end of let instance = new classes[mapClass.class]

Rannie Aguilar Peralta · Accepted Answer · 2019-05-09 07:17:06Z

1

You should use brackets. Just like how you access an item in an array

global[mapClass.class][mapClass.method]()

answered May 9, 2019 at 7:17

Rannie Aguilar Peralta

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