Using bracket notation depending on input data

Question

I'm in the process of optimizing some code in my library, however, I have a bit of an issue regarding why bracket notation isn't working when trying to call an imported class.

Parameter type accepts a string that is camelCased, such as: myString. The parameter data can be anything.

import { foo } from './example';

export const find = (type: string, data: any) => {

// This next line effectively deletes the end of the string starting
// from the first capital letter.
    const f = type.replace(/[A-Z][a-z]+/, '');
    try {
        return [f][type](data);
    } catch (e) {
        return e;
    }
};

this is what I expect it to look like if I was to visualize it using dot notation:

foo.fooBar(someRandomData)

This should call the static method fooBar(data) on the imported class foo, however, I receive an error message:

TypeError: [f][type] is not a function

If I was to revert it back to my if..else if style, it works:

if (type.startsWith('foo')) return foo[type](data);

How can I do what is desired above without getting the defined error message?

Thank you for your help in advance!

EDIT: This is an example I modified from already existing code, therefore, I fixed a few typos.

EDIT #2: as per requested, the imported class foo looks like this:

export class foo{
static fooBar(data){
// Do stuff with data...
}

This is unclear to me. What are you trying to accomplish with the [f][type] syntax? Because what you're doing is creating an array containing f, then trying to access the property named type from said array, which is probably returning undefined, which is not a function. — kevin.groat
– kevin.groat, Commented Jun 5, 2019 at 0:50
First, you should probably not use "type" like this, considering it is a keyword. Second, type is a string, and you are trying to use it like an array of functions. Third, I don't see any reference to foo. How does foo relate to your code above? Could you also include the code for foo (the "example" file)? — Jeremy
– Jeremy, Commented Jun 5, 2019 at 0:52
Are you trying to say that if your type string is, for instance 'fooBar', then it should call foo.bar(data)? — kevin.groat
– kevin.groat, Commented Jun 5, 2019 at 0:56
the end goal is to access the correct imported class (because there's more than one class, but not in this example) so that is why I have it structured like [class][method](data) so I can dynamically call the correct class without having to do a bunch of if statements. Unless this isn't possible and I'm missing something..? — Extevious-V
– Extevious-V, Commented Jun 5, 2019 at 1:02
Here is a post about exporting a static class - from your code sample I don't see anything wrong with what you did: stackoverflow.com/questions/16207593/…. — Jeremy
– Jeremy, Commented Jun 5, 2019 at 1:08

Jeremy · Accepted Answer · 2019-06-05 01:31:59Z

0

In the end you need some reference to the classes or object to get started with. Here is a working example of how you could do this type of functionality, but you have start with a map of your class instances so you can get to them:

class foo {
    fooBar(data: any) { return { name: 'foo', data } };
}

class example {
    exampleFood(data: any) { return { name: 'example', data } };
}

var lookup: { [classes: string]: any; } = { };
lookup['foo'] = new foo();
lookup['example'] = new example();

const find = (encodedType: string, data: any) => {
    // This next line effectively deletes the end of the string starting
    // from the first capital letter.
    const f = encodedType.replace(/[A-Z][a-z]+/, '');
    try {

        return lookup[f][encodedType](data);
    } catch (e) {
        return e;
    }
};

alert(JSON.stringify(find("fooBar", "Found you foo")));
alert(JSON.stringify(find("exampleFood", "Found you example")));

answered Jun 5, 2019 at 1:31

Jeremy

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1 Comment

Extevious-V Over a year ago

Thank you, this is a much better option than using conditional statements as what you did was key/value the classes in lookup. I will be using a slightly modified version, so I thank you for this!

kevin.groat · Accepted Answer · 2019-06-05 01:43:04Z

I would suggest you instead move over to using the nodeJS built-in EventEmitter.

You can do something like:

import * as EventEmitter from 'events';

import { foo } from './example';
import { bar } from './example2';

export const discordEventEmitter = new EventEmitter();

discordEventEmitter.on('fooBar', foo.fooBar);
discordEventEmitter.on('fooToo', foo.fooToo);
discordEventEmitter.on('barBell', bar.barBell);

Then, when you want to fire an event, you can simply:

discordEventEmitter.emit('fooBar', someData);

You can also simplify the event handler registration by writing:

const fooProps = Object.getOwnPropertyNames(foo) as (keyof typeof foo)[];
fooProps.filter(k => typeof foo[k] === 'function').forEach(funcName => {
  discordEventEmitter.on(funcName, foo[funcName]);
});

const barProps = Object.getOwnPropertyNames(bar) as (keyof typeof bar)[];
fooProps.filter(k => typeof bar[k] === 'function').forEach(funcName => {
  discordEventEmitter.on(funcName, bar[funcName]);
});

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