Chapter quiz · Functions

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8 questions on Functions. Pass 70% to clear the chapter.

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Quiz

Functions — Chapter Quiz

Eight questions on function declarations, parameters, arrows, scope, closures, this.

0/ 10

Question 1
1
Which is the most important difference between a function declaration and a function expression?
ADeclarations can have parameters; expressions cannotBDeclarations are hoisted; expressions are notCExpressions can return values; declarations cannotDThere is no difference — they are identical
Function declarations are hoisted — you can call them before the line where they're written. Function expressions aren't.
Question 2
2
What does this code log?
```
function add(a, b = a) {
  return a + b;
}
console.log(add(5));
```
A5B10CNaNDTypeError
b defaults to a (which is 5). So add(5) returns 5 + 5 = 10.
Question 3
3
What does this code log?
```
function sum(...nums) {
  return nums.length;
}
console.log(sum(1, 2, 3, 4));
```
A4B1C10D[1, 2, 3, 4]
...nums gathers all arguments into an array. The array has 4 items, so nums.length is 4.
Question 4
4
An arrow function gets its own this, separate from the surrounding scope.
TTrueFFalse
Arrow functions DON'T get their own this. They inherit it from the enclosing scope. This is one of the most important differences from regular functions.
Question 5
5
After for (var i = 0; i < 3; i++) setTimeout(() => console.log(i));, what gets logged?
A0, 1, 2B3, 3, 3C0, 0, 0Dundefined, undefined, undefined
var is function-scoped, so all three callbacks close over the SAME i. By the time the callbacks run, i is 3. Replace var with let to get 0, 1, 2.
Question 6
6
What does this code log?
```
const user = {
  name: "Ada",
  greet() {
    return `Hi, ${this.name}`;
  },
};
const fn = user.greet;
console.log(fn?.());
```
A"Hi, Ada"B"Hi, undefined"CTypeErrorDundefined
The "lost this" bug. fn = user.greet detaches the method. Calling fn() plainly means this is undefined. this.name becomes undefined.name — which would crash, but we used optional access so the template just prints "undefined".
Question 7
7
What does .bind(obj) do to a function?
ACalls the function immediately with this = objBReturns a new function with this permanently set to objCModifies the original function so its this is objDRemoves this from the function entirely
bind doesn't invoke — it returns a NEW function with this fixed. The original is unchanged. call and apply invoke immediately.
Question 8
8
A function that takes another function as an argument or returns a function is called a _________ function.
Higher-order function. The pattern is everywhere in JavaScript — map, filter, reduce, event listeners, factories.