Accessing instance variable inside of a callback function

Question

What I'm trying to do is pretty trivial: I am creating an object, or better I'm defining a function that is instantiating the object, and then I have another function that reads from a file and gets a callback when the reading is finished. The function is assigned to the prototype of the object, so that it's created only once and not every time I'm creating a new instance of it.

var fs = require('fs');

var CrazyObject = function () {
    this.craziness = 'this is sooo crazy';
};

CrazyObject.prototype.crazyFunction = function (file) {
    fs.readFile(file, function (err, result) {
        // here i can't access the craziness!
    });

    // but here i can
};

exports.CrazyObject = CrazyObject;

As the example shows, the problem is that inside the callback I can't access the variable assigned when the object is created.

Well since the value can change it's still a variable :) semantically speaking of course. — Alessandro Roaro, Feb 29 '16 at 21:23

score 3 · Accepted Answer · answered Feb 29 '16 at 21:13

3

Just bind your callback function to the correct context:

fs.readFile(file, (function (err, result) {
    console.log(this.craziness);
}).bind(this));

answered Feb 29 '16 at 21:13

madox2

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It was trivial indeed. Thanks! – Alessandro Roaro Feb 29 '16 at 21:36

Accessing instance variable inside of a callback function

1 Answers1