JavaScript `bind` not working on imported functions/objects

Question

There are three files.

context.js which exports an object passed to bind:

module.exports = {
    exceptionValue: 99
};

strategy.js that is exports the function I want to call bind on:

module.exports = events => {
    if (this.exceptionValue !== 99) {
        throw new Error(this);
    }
    return events;
};

index.js which imports both the previous files:

const context = require('./context');
const strategy = require('./strategy');

const strategyWithContext = strategy.bind(context);
return strategyWithContext(events);

events is a list of JSON objects that are passed to index.js. To be more precise, I'm exporting this function from index.js and people who call it will provide those events. But it's nothing special, just a list of JSON objects.

The problem is that the this reference inside the strategy function isn't working and it's always throwing an exception. I can't access my context object at all. What am I doing wrong? Why isn't it working?

What behavior are you seeing? Where is events defined in index.js? — Will, Apr 16 '19 at 16:10
Check this link https://stackoverflow.com/questions/33308121/can-you-bind-arrow-functions — lankovova, Apr 16 '19 at 16:13
Arrow functions were created to keep the context they were created in. They don't bind to contexts. Use non arrow functions for this. — Snapstromegon, Apr 16 '19 at 16:14
@lankovova is right, you cannot bind an arrow function anyway. — Will, Apr 16 '19 at 16:14

score 6 · Answer 1 · answered Apr 16 '19 at 16:14

6

You've misidentified the problem. The export is irrelevant.

Arrow functions already bind a this value, and you can't override it with bind().

Use a function expression instead of an arrow function.

module.exports = function (events) {
    if (this.exceptionValue !== 99) {
        throw new Error(this);
    }
    return events;
};

answered Apr 16 '19 at 16:14

Quentin

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completely right answer. Helped me a lot. Spent half of day. Thank you Quentin! – Sergey Oct 16 '19 at 14:05

JavaScript `bind` not working on imported functions/objects

1 Answers1