The execution of a nested object's function that calls a JavaScript function encounters an error

Question

The execution of a nested object's function that calls a JavaScript function encounters an error

Below is a simple example demonstrating the issue I am facing, which you can also view on JSFiddle here.

While I understand why the issue is happening, I'm unsure of how to resolve it without altering the existing JS structure.

The problem arises when defining prototype functions for JavaScript objects, particularly when there is a nested object at the 2nd level that contains a function calling another function on the parent/root level. This leads to a failure in execution.

In the code snippet provided, the line

this.nestedObject.nested_object_function()

is attempting to invoke the function this.normal_function(), resulting in the error:

Uncaught TypeError: this.normal_function is not a function
    at Object.nested_object_function (VM2493:79)

It seems that the issue stems from this referencing this.nestedObject instead of the parent object.

If this assumption is correct, how can I successfully call the desired function from within the nested object function and access a function from the parent object?

I have also experimented with calling JsLibTest.normal_function() as a test within the

this.nestedObject.nested_object_function()

function, but encountered the same error.

    var JsLibTest = (function (document) {
        "use strict";
    
        var JsLibTest = function (){
          this.init();
        };
    
        JsLibTest.prototype = {
    
          init: function() {
    
            this.normal_function();
    
            this.nestedObject.nested_object_function();
    
          },
    
          normal_function: function() {
              console.log('this.normal_function() ran');
          },
    
          nestedObject: {
          
              nested_object_function: function() {
              this.normal_function();
                console.log('this.nestedObject.nested_object_function() ran');
              },
          }
    
        };
    
        return JsLibTest;
    })(document);
    
    $(document).ready(function(){
      var Sidebar2 = new JsLibTest();
    });

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

javascript

Answer 1

Answer №1

Your understanding is accurate. When referencing this in a nested object, it will point to the nested object itself rather than the parent object, resulting in the function being deemed undefined.

To solve this issue, you need a method to access the parent object. Typically, objects do not inherently contain information to reference objects that reference them. This is logical considering multiple objects may internally reference the same object.

One approach is to store a reference to the parent object and utilize it in the nested function:

var nested = {
  g() {
    this.parent.f();
  }
};
var parent = {
  f() {
    console.log('called');
  }
};
nested.parent = parent;

nested.g();

Alternatively, you can employ Function.prototype.call (or a similar method) to establish the correct context.

var obj = {
  f() {
    console.log('called');
  },
  g() {
    this.nested.nested_f.call(this);
  },
  nested: {
    nested_f() {
      this.f();
    }
  }
};

obj.g();

Applying the latter solution within the context of your scenario:

var JsLibTest = (function(document) {
  "use strict";

  var JsLibTest = function() {
    this.init();
  };

  JsLibTest.prototype = {

    init: function() {
      this.normal_function();

      // Utilizing .call here to specify the context
      this.nestedObject.nested_object_function.call(this);
    },


    normal_function: function() {
      console.log('this.normal_function() executed');
    },

    nestedObject: {
      nested_object_function: function() {
        this.normal_function();
        console.log('this.nestedObject.nested_object_function() executed');
      }
    }
  };

  return JsLibTest;
})(document);

// invoke it
$(document).ready(function() {
  var Sidebar2 = new JsLibTest();
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Answer 2

Your understanding is accurate. When referencing this in a nested object, it will point to the nested object itself rather than the parent object, resulting in the function being deemed undefined.

To solve this issue, you need a method to access the parent object. Typically, objects do not inherently contain information to reference objects that reference them. This is logical considering multiple objects may internally reference the same object.

One approach is to store a reference to the parent object and utilize it in the nested function:

var nested = {
  g() {
    this.parent.f();
  }
};
var parent = {
  f() {
    console.log('called');
  }
};
nested.parent = parent;

nested.g();

Alternatively, you can employ Function.prototype.call (or a similar method) to establish the correct context.

var obj = {
  f() {
    console.log('called');
  },
  g() {
    this.nested.nested_f.call(this);
  },
  nested: {
    nested_f() {
      this.f();
    }
  }
};

obj.g();

Applying the latter solution within the context of your scenario:

var JsLibTest = (function(document) {
  "use strict";

  var JsLibTest = function() {
    this.init();
  };

  JsLibTest.prototype = {

    init: function() {
      this.normal_function();

      // Utilizing .call here to specify the context
      this.nestedObject.nested_object_function.call(this);
    },


    normal_function: function() {
      console.log('this.normal_function() executed');
    },

    nestedObject: {
      nested_object_function: function() {
        this.normal_function();
        console.log('this.nestedObject.nested_object_function() executed');
      }
    }
  };

  return JsLibTest;
})(document);

// invoke it
$(document).ready(function() {
  var Sidebar2 = new JsLibTest();
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Answer 3

Answer №2

It is important to note that the scope does not have direct access to the parent. One way to solve this issue is by passing the parent to the nested object. Here's how you can do it:

this.nestedObject.nested_function(this);

Then, in your nested function, you can refer to the parent like this:

nested_function: function(self) {
    self.some_function();
    alert('this.nestedObject.nested_function() was executed');
}

By passing 'this' (parent) as 'self', you can effectively call it from the nested function.

Answer 4

It is important to note that the scope does not have direct access to the parent. One way to solve this issue is by passing the parent to the nested object. Here's how you can do it:

this.nestedObject.nested_function(this);

Then, in your nested function, you can refer to the parent like this:

nested_function: function(self) {
    self.some_function();
    alert('this.nestedObject.nested_function() was executed');
}

By passing 'this' (parent) as 'self', you can effectively call it from the nested function.

Answer 5

Answer №3

To start, it is important that each Object is distinct and has its own prototype:

this.childObject = Object.create(this.childObject);

var CustomLibraryTest = function() {
      // execute init() function when a new CustomLibraryTest object is created
      this.init();
      // establish parent-child relationship:
      this.childObject.parent = this;
    };

Now, you can reference this.parent within your inner function...

this.parent.custom_function();

If you wish for this to serve as the parent, utilize binding:

var CustomLibraryTest = function() {
      // execute init() function when a new CustomLibraryTest object is created
      this.init();
      // establish parent-child relationship:
      for(i in this.childObject) {
         var element = this.childObject[i];
         if(typeof element === "function") {
             this.childObject[i] = element.bind(this);
         }
       }
    };

For convenience, you can utilize a helper function like this:

getFunction: function(...args) {
  args.reduce((object, key) => object[key], this).bind(this);
}

Usage example:

CustomLibraryTestInstance("childObject", "childobject_function")();

Answer 6

To start, it is important that each Object is distinct and has its own prototype:

this.childObject = Object.create(this.childObject);

var CustomLibraryTest = function() {
      // execute init() function when a new CustomLibraryTest object is created
      this.init();
      // establish parent-child relationship:
      this.childObject.parent = this;
    };

Now, you can reference this.parent within your inner function...

this.parent.custom_function();

If you wish for this to serve as the parent, utilize binding:

var CustomLibraryTest = function() {
      // execute init() function when a new CustomLibraryTest object is created
      this.init();
      // establish parent-child relationship:
      for(i in this.childObject) {
         var element = this.childObject[i];
         if(typeof element === "function") {
             this.childObject[i] = element.bind(this);
         }
       }
    };

For convenience, you can utilize a helper function like this:

getFunction: function(...args) {
  args.reduce((object, key) => object[key], this).bind(this);
}

Usage example:

CustomLibraryTestInstance("childObject", "childobject_function")();

Answer 7

Answer №4

Ah yes, it is indeed correct that the this value within the JSLibTest.prototype.nestedObject function is referencing the nestedObject itself and not the JSLibTest object.

If you wish to keep the same call signature, you can define nestedObject as an immediately invoked function expression (IIFE):

nestedObject: (function() {
  var that = this;

  return {
    nested_object_function: function() {
      console.log(that);
      // this.normal_function();
      alert('this.nestedObject.nested_object_function() was executed');
    }
  }
}())

https://jsfiddle.net/dnLzytju/1/

Please note: It may not be advisable to define your prototype in this manner as it essentially removes all the built-in prototype methods of the object.

If you want to structure your code similarly, you could utilize Object.assign to assist you:

var foo = Object.assign({}, Function.prototype, {
  bar() {
    console.log("Hello!")
  }
});

foo.bar();

Answer 8

Ah yes, it is indeed correct that the this value within the JSLibTest.prototype.nestedObject function is referencing the nestedObject itself and not the JSLibTest object.

If you wish to keep the same call signature, you can define nestedObject as an immediately invoked function expression (IIFE):

nestedObject: (function() {
  var that = this;

  return {
    nested_object_function: function() {
      console.log(that);
      // this.normal_function();
      alert('this.nestedObject.nested_object_function() was executed');
    }
  }
}())

https://jsfiddle.net/dnLzytju/1/

Please note: It may not be advisable to define your prototype in this manner as it essentially removes all the built-in prototype methods of the object.

If you want to structure your code similarly, you could utilize Object.assign to assist you:

var foo = Object.assign({}, Function.prototype, {
  bar() {
    console.log("Hello!")
  }
});

foo.bar();

The execution of a nested object's function that calls a JavaScript function encounters an error

Answer №1

Answer №2

Answer №3

Answer №4

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