Output Quiz #4 — this Binding & Arrow Functions

Output:

true

Why: When a regular function is called as a plain function call (no object, no call/apply/bind, not new), this defaults to the global object (window in browsers, globalThis in Node). In strict mode ("use strict"), default binding sets this to undefined instead.

Output:

Alice

Why: When a function is called as a method on an object (obj.greet()), this is implicitly bound to the object to the left of the dot — obj. So this.name is obj.name, which is "Alice".

Output:

undefined

Why: fn = obj.greet copies the function reference but loses the binding. When fn() is called as a plain function (no object before the dot), this falls back to default binding — the global object in non-strict mode. globalThis.name is undefined (or an empty string in browsers). The method hasn't changed; only how it was called has changed.

Output:

Bob

Why: Function.prototype.call(thisArg, ...args) explicitly sets this for that one invocation. greet.call(user) calls greet with this === user, so this.name is "Bob".

Output:

true

Why: Arrow functions do not have their own this. They capture this from their enclosing lexical scope at the time they are defined. greet is defined at the top level (inside an object literal, but the object literal doesn't create a new scope), so the enclosing this is globalThis. Calling obj.greet() doesn't change anything — the object-method binding rule doesn't apply to arrow functions.

Output:

Dave

Why: outer is a regular function — when called as obj.outer(), this is bound to obj. The arrow function inner is defined inside outer, so it inherits this from outer's scope, which is obj. Calling inner() as a plain function doesn't override the inherited this.

Output:

Eve

Why: bind returns a new function with this permanently set to user. You cannot override the binding of a bound function with call, apply, or another bind. Even though boundGreet.call(other) tries to set this to other, the original bind wins.

Output:

TypeError

Why: Class bodies run in strict mode. When tick is extracted and called as a plain function, this is undefined (strict mode default binding). Accessing undefined.count throws a TypeError. This is the common bug when passing class methods as callbacks (e.g., to addEventListener or setTimeout) without binding them first.

Output:

Grace
true

Why: When a function is called with new, four things happen: a new object is created, this is bound to that new object, the function body runs (setting this.name), and the new object is returned implicitly (unless the function returns another object explicitly). new binding takes priority over all other binding rules.

Output:

1
undefined

Why: obj.fn() uses implicit binding (object-method call), but bound is already hard-bound via .bind({ x: 1 }) — implicit binding loses to bind. So this.x is 1. new bound() creates a brand new object for this — new does override bind's target, so this is the freshly created empty object, which has no x property → undefined.