The 'this' Keyword

The `this` keyword in JavaScript is a frequent source of confusion because its value is determined by how a function is called, not where it is defined. This is known as dynamic context. There are four main rules for determining the value of `this`. First, in the global context (outside of any function), `this` refers to the global object (`window` in browsers, `global` in Node.js). Second, when a function is called as a method of an object (`object.method()`), `this` inside that method refers to the object itself. This is the most intuitive use case. Third, when a function is called as a standalone function (e.g., `myFunction()`), `this` will default to the global object in non-strict mode, and will be `undefined` in strict mode. This is a common pitfall. Fourth, when using `call`, `apply`, or `bind`, you can explicitly set the value of `this` for a function call. ES6 arrow functions introduced a fifth behavior: they do not have their own `this` binding and instead inherit it from their parent (lexical) scope. Understanding these rules is critical for object-oriented programming in JavaScript and for debugging issues where `this` does not refer to what you expect.