18 Questions
What does the JavaScript Array object store?
Multiple data types under a single variable name
When using the map() method in JavaScript, what is the purpose of the callback function?
To transform each element in the array
Which JavaScript data type is considered a primitive?
Symbol
What is the main characteristic of a loosely typed language like JavaScript?
Variables can change data types during execution
In React, what does 'render element' typically refer to?
A piece of JSX code defining a component for display
When using the filter() method in JavaScript, what is the purpose of the callback function?
To remove elements based on a condition
What is the value returned by reduce() when used without an initial value?
The last element of the array
In JavaScript, a class is like a __________ for creating objects.
Blueprint
Which method is automatically called when a new object of a class is created in JavaScript?
Constructor()
What data types are defined as properties in the given JavaScript class example?
Strings
Which React concept involves the extraction of multiple components to organize code efficiently?
Fragments
Which array transformation method is not mentioned in the provided context?
[0]
What is the purpose of the Virtual DOM in React?
To hold the updates made by the user and reflect them to the original DOM
Which method in ReactDOM is used to render a single React component?
render()
Why are React elements considered immutable?
Because they can't change their children or attributes
What does it mean when it's mentioned that a React element is like a single frame in a movie?
It represents the UI at a certain point in time and cannot be altered
Which ReactDOM method is used to unmount a React component from a specific DOM node?
unmountComponentAtNode()
How many root DOM nodes do applications built with just React usually have?
One
Study Notes
JavaScript Data Types and Data Structures
- JavaScript is a loosely typed language, meaning variables are not assigned to a particular data type.
- There are eight data types in JavaScript: seven primitives (String, Number, Boolean, Undefined, Null, BigInt, Symbol) and one non-primitive (JavaScript object).
- JavaScript objects include Arrays, Objects, Functions.
JS Array Methods
- The Array object stores a collection of multiple items under a single variable name.
- Array methods include Map, Filter, Reduce.
- The Map() method:
- Maps an array of numbers using a function containing an argument.
- Returns a new array with each element being the result of the callback function.
- The Reduce() method:
- Can be used with or without an initial value.
- The array parameter never changes during the process.
- The value returned by reduce() is that of the last callback invocation.
Lists in React
- The Map() method can be used to reformat objects in an array.
- In React, the map method is used to transform lists, and a key is required for each item.
- Multiple components can be extracted, with a component tree.
JS Classes
- A class in object-oriented programming is like a blueprint or template for creating objects.
- A class should be defined before using it, and it is not hoisted.
- A JavaScript class is not an object, but a template for JavaScript objects.
- Properties and methods can be defined in a class, such as a Constructor() method.
Using a Class
- A class can be used to create objects, with the constructor method called automatically when a new object is created.
- React updates the Virtual DOM relative to the components, runs the diffing algorithm, and updates the real DOM.
React DOM
- The Virtual DOM is a copy of the actual DOM representation, used to hold updates made by the user and reflect them over to the original Browser DOM.
- ReactDOM provides DOM-specific methods, including render(), findDOMNode(), unmountComponentAtNode(), hydrate(), and createPortal().
- The render() function is used to render a single React Component, or several Components wrapped together.
- A "root" DOM node is used to manage everything inside it, and can be used in applications built with just React or when integrating React into an existing app.
Test your knowledge on data types and data structures in JavaScript. Learn about the different primitives like string, number, boolean, and more. Explore JavaScript objects including arrays, objects, and functions.
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