Prototype vs Constructor Methods in JavaScript: Is One Really Faster?

Defining Methods in JavaScript: Performance Differences between Prototype vs Constructor

In JavaScript, there are two approaches to defining public methods for classes: via the prototype or using the constructor function. While the prototype approach is said to be more efficient due to shared function references, there's a potential performance impact to consider.

Method 1: Defining Methods via Prototype

function MyClass() {
    var privateInstanceVariable = 'foo';
    this.myFunc = function() { alert(privateInstanceVariable ); }
}

In this method, each instance of the class has its own private instance variable and its own copy of the myFunc method.

Method 2: Defining Methods Using Constructor

function MyClass() { }

MyClass.prototype.myFunc = function() { alert("I can't use private instance variables. :("); }

Here, the myFunc method is defined on the class prototype. All instances share the same function reference, potentially improving performance.

Performance Considerations

According to a JavaScript performance test (https://jsperf.app/prototype-vs-this), declaring methods via the prototype is indeed faster. However, the significance of this difference is questionable.

Unless you're creating and destroying thousands of objects repeatedly, the performance impact is likely negligible. In most cases, using the approach that makes more sense for your code readability and maintainability is more important.

Private Instance Variables

It's important to note that while Method 1 supports private instance variables, they are only considered conventionally private. Developers can still access them if they wish. To protect variables from outside access, consider declaring them with a leading underscore (e.g., _process()) or implementing custom getters and setters to enforce encapsulation.

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