Let’s examine how the extends clause influences how a class is set up ( Sect. Then it doesn’t matter whether this is initialized or not. If a constructor explicitly returns an object, it is used as its result.To follow this ES6 tutorial, you should have a good knowledge of JavaScript up to ES5. It is the first major update to the language since ES5 which was standardized in 2009. If this is uninitialized, a TypeError is thrown. ES6 Tutorial ECMAScript 2015 or ES2015 is a significant update to the JavaScript programming language. If a constructor explicitly returns a non-object (including undefined and null), the result is this (this behavior is required to remain compatible with ES5 and earlier).This protects you against forgetting to call super(). If this is uninitialized, a ReferenceError is thrown. If a constructor returns implicitly (without a return statement), the result is this.This protects you against calling super() twice. Once this is initialized, calling super() produces a ReferenceError.this originally being uninitialized in derived constructors means that an error is thrown if they access this in any way before they have called super().How do I instantiate a class, given an Array of arguments?Ĭlass Stack extends Array Employee. Complaint: Classes lock you in, due to mandatory new Complaint: Classes provide only single inheritance Complaint: ES6 classes obscure the true nature of JavaScript inheritance Overriding the default species in subclasses Why can’t you subclass built-in constructors in ES5? Private data via constructor environments
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