JavaScript Array Destructuring and Defaults

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Given the following code snippet, what will be the value of a and b after the code is executed?

let a = 111;
let b = 999;
const obj = { a: 23, b: 7, c: 14 };
({ a, b } = obj);

a = 23, b = 999

a = 23, b = 7 (correct)

a = 111, b = 7

a = 111, b = 999

In JavaScript, the spread operator(...) can be used for passing separated data of an ________ into a function.

array

Consider the following JavaScript code:

const nested = [1, [2, 3], 4];
const [a, [b, c], d] = nested;
console.log(a, b, c, d);

What will be the output of console.log(a, b, c, d)?

1, 2, 3, 4 (correct)

1, 2, undefined, 4

Error: Invalid destructuring assignment

1, [2, 3], undefined, 4

The spread operator (...) can be used to create a deep copy of an object in JavaScript.

False (B) Signup and view all the answers

Describe how array destructuring can be used to swap the values of two variables `a` and `b` in JavaScript. Include a brief code example.

Array destructuring allows swapping variable values without a temporary variable. <code>[a, b] = [b, a];</code> Signup and view all the answers

Given the following code:

`const HP = ['harry','hermion','ron',...['dambeldor','Snape','mackgolagan']]; const [name,...rest] = HP;`

What will `console.log(rest)` output?

<code>['hermion', 'ron', ['dambeldor', 'Snape', 'mackgolagan']]</code> (C) Signup and view all the answers

The spread operator can be used on non-iterable objects directly without creating a new array.

False (B) Signup and view all the answers

Explain the difference between the `||` operator and the `??` (nullish coalescing) operator in JavaScript, particularly focusing on what values they consider 'falsy'.

The <code>||</code> operator returns the first truthy value. It considers <code>0</code>, <code>''</code>, <code>null</code>, <code>undefined</code>, <code>NaN</code>, and <code>false</code> as falsy. The <code>??</code> operator returns the first value that is not nullish (i.e., not <code>null</code> or <code>undefined</code>). Signup and view all the answers

In the context of function parameters, the ______ parameter must always be the last one defined.

rest Signup and view all the answers

Match the operator with its description:

<code>...</code> (spread operator) = Expands an iterable (like an array) into individual elements. <code>...</code> (rest parameter) = Collects multiple elements into a single array. <code>||</code> = Returns the first truthy value. <code>??</code> = Returns the first non-nullish value (null or undefined). Signup and view all the answers

What is the index and value that will be logged to the console for the second element in the following code snippet?

`const arr = ['Newt', 'Tina', 'Jacob Kowalski', 'Queenie']; for(const item of arr.entries()) {console.log(item)}`

<code>[1, 'Tina']</code> (D) Signup and view all the answers

In enhanced object literals, the shorthand for assigning a property named `seasons` with the value of the variable `seasons` is simply `_________`.

seasons Signup and view all the answers

Consider the following code: `const seasonNum = [1,2,3,4,5]; const seasons = { [seasonNum]: { episode: 13, realeased: {First: '20 September 2008', Last: '13 December 2008'} } };` What does `seasons[seasonNum].episode` evaluate to?

<code>13</code> (C) Signup and view all the answers

The following code snippet will cause an error because the seasonNum array is used as a property key:

`const seasonNum =[1,2,3,4,5]; const seasons = { [seasonNum]: { episode:13, realeased:{First:'20 September 2008 ', Last:'13 December 2008'} } };`

False (B) Signup and view all the answers

In the `serie` object, how is the `getInfo` method defined using ES6 syntax, and what does it log to the console?

getInfo(){ console.log(<code>it is ${this.name}.it has a ${this.type} story.the main copel are ${</code>) } Signup and view all the answers

Which of the following statements accurately describes the behavior of the nullish coalescing operator (`??`) in JavaScript, as demonstrated by the example `serie.risoto?.(10,12) ?? console.log('the method does not exist');`?

It executes <code>console.log('the method does not exist')</code> only if <code>serie.risoto</code> is <code>null</code> or <code>undefined</code>, preventing a potential error when calling a non-existent method. (B) Signup and view all the answers

Given the code:

const openinghours = {
  sat: { open: '10 am', close: '10 pm' },
  sun: { open: '11 am', close: '9 pm' },
  mon: { open: '6 am', close: '12 pm', shift: 'harry' }
};

const values = Object.values(Object.keys(Object.values(openinghours)));
console.log(values);

The values variable will contain an array of the opening and closing times for each day.

False (B) Signup and view all the answers

Explain how the concept of optional chaining (`?.`) and nullish coalescing (`??`) operators can be combined to safely access nested object properties and provide a default value if the property is missing.

Optional chaining (<code>?.</code>) allows you to safely access properties of an object that may be <code>null</code> or <code>undefined</code> without causing an error. Nullish coalescing (<code>??</code>) then provides a default value if the result of the chained property access evaluates to <code>null</code> or <code>undefined</code>. For example: <code>obj?.prop1?.prop2 ?? 'default'</code>. Signup and view all the answers

In JavaScript, the `Object.entries()` method returns an array of a given object's own enumerable string-keyed property `______`, in the format `[key, value]`.

pairs Signup and view all the answers

Match the following JavaScript code snippets with their described outcomes:

<pre><code class="language-javascript">const singers = new Set(['NF','lady gaga','NF']); console.log(singers.size); ``` = Outputs the number of unique elements in a Set ```javascript const journey=new Map(); journey.set('paris','24 journey 2020'); console.log(journey.has('paris')); ``` = Outputs true if the key exists; otherwise, false. ```javascript const obj = {a: 1, b: 2}; for (const k of Object.keys(obj)) { console.log(k); } ``` = Iterates through the keys of an object. ```javascript const singers = new Set(['NF']); const topSingers=[...singers]; console.log(topSingers); ``` = Converts a Set to an Array. </code></pre> Signup and view all the answers

Flashcards

Array Destructuring

A feature to unpack values from arrays into distinct variables.

Default Values in Destructuring

Assign default values when the array elements are undefined.