While working on some javascript code, I found myself extending built-in classes and overriding methods with my own versions. However, I encountered a problem where sometimes I needed to access the original methods within my overridden ones, but JavaScript did not always allow me to do so. This inconsistency led to unpredictable behavior that left me confused about what was happening.
An example of this inconsistent behavior can be seen in the modified replace method of a built-in JavaScript class:
//Extending the String class to create a new class called STRING.
class STRING extends String
{
//Overriding the original 'replace' method.
replace()
{
//Attempting to access the original 'replace' method by traversing the prototype chain. However, the results are not consistent.
return this.__proto__.__proto__.replace.call(this);
}
}
//Replacing the original 'replace' method with the custom one in the String prototype.
String.prototype.replace = STRING.prototype.replace;
//Replacing the entire String class with the custom STRING class.
String = STRING;
//Creating a custom string primitive.
let a = "hello stacky";
//Calling the custom replace method on the custom string primitive.
a.replace();
In essence, this code acts as a proxy for the default behaviors of the String class and its replace method, passing them through my custom implementation. Although seemingly unnecessary, this simplified example highlights the issue at hand.
Despite the missing elements and trivial nature of this code snippet, it serves its purpose in showcasing the problem I'm facing. We'll ignore the absence of parameters for the replace method for now, as the function behaves similarly to toString when called without arguments.
After defining the STRING class as an extension of String, I ensure that the replace method is available to all types of strings – constructed using STRING, String, or literal syntax.
The inconsistencies arise when attempting to access the original replace method from the String superclass within the extended STRING class definition.
- When the logic works as expected:
thispoints to the current instance of theSTRINGobject.this.__proto__refers to the prototype of theSTRINGobject.this.__proto__.__proto__should resolve to the prototype of the prototype, i.e., the original JavaScriptStringclass.
- Contrastingly, when the behavior is erratic:
- The chain of
this.__proto__references leads back to theObjectclass instead of the desiredStringclass.
- The chain of
A failed attempt to access the correct method using super instead of manual chaining results in a typeError indicating undefined property.
These discrepancies have prompted confusion over why this code worked previously but now presents issues. Could it be related to the beta (unstable) version of MongoDB being used for testing?
The overarching task is to define a subclass of the String class that overrides the replace method while ensuring consistent behavior across all string instances. How can this goal be achieved effectively?