Question

I’m creating a small lib to interact with MongoLab HTTP API, but I’m having some issues. I’m using CommonJS modules.

I have a Model object, made to behave as prototype for the other models:

module.exports = {
    //[...]

    //this will be overriden by the other models
    fields: ['id'],

    setFields: function(values) {
        _.each(this.fields, function(field) {
            this[field] = values[field]
        })
    }
}

And I have, for example, an User model:

var Model = require('models/Model')

function User (properties) {

    this.fields = [
        'id',
        'name',
        'surname',
        'email',
        'password'
    ]

    this.setFields(properties)

    //[...]
}

There, the setFields() call works correctly, iterating through each of the five fields given in the User model; although, it won’t set the User properties. If I add a console.log(this.name) before the end of the setFields() definition, it will give me undefined. The only way I got to workaround the issue was passing the this object as argument for the setFields method, and using the argument instead of this.

It looks like a scope problem for me, but I’m still quite new with JavaScript OO, so… What’s wrong with my logic?

Answer 1

You need to provide a context parameter to _.each to set the this context you’re expecting in your callback function:

setFields: function(values) {
    _.each(this.fields, function(field) {
        this[field] = values[field];
    }, this);  // context parameter that establishes this in your callback
}