TypeError: Cannot set property "STRING" of undefined at STRING (Javascript)

Question

I have this "class":

function BooleanAssoc(keyNames) {
    this.assoc = {};
    $.each(keyNames, function(i, val) {
        this.assoc[val] = false;
    });
};

I use it like this:

var signUpStates = new BooleanAssoc([
    "CNPJ", 
    "PASSWORDS", 
    "ADDRESS", 
    "GENERAL_FIELDS", 
    "STATE", 
    "CITY", 
    "SEGMENT", 
    "PRODUCT",
    "EMAIL",
    "TERMS"
]);

I don't understand why I get a TypeError. Perhaps it's my mind that is too "pythonic". I create a dictionary ("Associative Array"), I iterate over a list of strings and create the keys and assign their values accordingly. What am I doing wrong??

Try binding the callback to $.each to this: $.each(key...(i, val){}.bind(this)). — Hunan Rostomyan
– Hunan Rostomyan, Commented Dec 1, 2015 at 4:07

Brendan Molloy · Accepted Answer · 2015-12-01 04:35:55Z

4

Your this is not the this you expect.

Try:

function BooleanAssoc(keyNames) {
  this.assoc = {};

  $.each(keyNames, function(i, val) {
    this.assoc[val] = false;
  }.bind(this));
};

ES5 environments you can just use .forEach too. If using ES6, you can use arrow functions which do not bind the this and use the parent scope:

function BooleanAssoc(keyNames) {
  this.assoc = {};

  keyNames.forEach(val => {
    this.assoc[val] = false;
  });
};

You can also do the following, although it is often considered to not be a best practice as it unnecessarily introduces variables into the scope. However, if you're in an environment like ES3, and where you cannot use shims to add ES5 features, the following will work:

function BooleanAssoc(keyNames) {
  var self = this;
  this.assoc = {};

  $.each(keyNames, function(i, val) {
    self.assoc[val] = false;
  });
};

edited Dec 1, 2015 at 4:35

answered Dec 1, 2015 at 4:09

Brendan Molloy

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Comments

Hunan Rostomyan · Accepted Answer · 2015-12-01 04:09:46Z

0

This should work:

function BooleanAssoc(keyNames) {
    this.assoc = {};
    $.each(keyNames, function(i, val) {
        this.assoc[val] = false;
    }.bind(this));
};

answered Dec 1, 2015 at 4:09

Hunan Rostomyan

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Comments

Deepak Jose · Accepted Answer · 2015-12-01 04:13:41Z

0

I think it is an issue with the context. Inside each this refers to the current value not the context of the class BooleanAssoc.

function BooleanAssoc(keyNames) {
    var self = this;
    self.assoc = {};
    $.each(keyNames, function(i, val) {
        self.assoc[val] = false;
    });
};

Try above one instead.

answered Dec 1, 2015 at 4:13

Deepak Jose

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