Podcast
Questions and Answers
What is a closure in JavaScript primarily used for?
What is a closure in JavaScript primarily used for?
What keyword is used to create a new object from a constructor function in JavaScript?
What keyword is used to create a new object from a constructor function in JavaScript?
How can closures be beneficial in constructor functions?
How can closures be beneficial in constructor functions?
What does the Document Object Model (DOM) represent in web development?
What does the Document Object Model (DOM) represent in web development?
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Which of the following best describes lexical scope in JavaScript?
Which of the following best describes lexical scope in JavaScript?
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What are nodes in the context of the Document Object Model?
What are nodes in the context of the Document Object Model?
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What is an Immediately Invoked Function Expression (IIFE)?
What is an Immediately Invoked Function Expression (IIFE)?
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Which of the following is NOT a reason for using closures in programming?
Which of the following is NOT a reason for using closures in programming?
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What is the purpose of the nodeType property in the DOM?
What is the purpose of the nodeType property in the DOM?
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Which method would you use to retrieve an element by its unique ID?
Which method would you use to retrieve an element by its unique ID?
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What does the getElementsByTagName() method return?
What does the getElementsByTagName() method return?
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How do you convert an HTMLCollection to an array?
How do you convert an HTMLCollection to an array?
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What does the querySelector() method do?
What does the querySelector() method do?
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Which selector does '*' represent in querySelector()?
Which selector does '*' represent in querySelector()?
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If you want to change the inner HTML of a paragraph element, which of the following would be correct?
If you want to change the inner HTML of a paragraph element, which of the following would be correct?
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What does the method getElementsByClassName() return?
What does the method getElementsByClassName() return?
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Study Notes
JavaScript Closures
- A closure in JavaScript is created when a function is defined inside another function.
- It retains access to variables from its parent function's scope, even after the outer function has finished executing.
- Closures allow a function to "remember" its creation environment, including variables in scope at that time.
- Lexical scope defines variable and function accessibility based on their location within the source code. A closure maintains a reference to its lexical environment, capturing the state of the outer function at its creation.
Closure Example
- A function (createCounter()) creates another inner function that uses variables declared in the higher-level function.
- The inner function is a closure.
- The inner function can access and modify variables in the outer function's scope.
Closure Use with Constructors
- JavaScript uses functions, called constructor functions, to create objects.
- A constructor function is defined, and the
new
keyword creates a new object from that function. - Inside the function,
this
is used to attach properties and methods to the new object.
Example of Constructor Function
- The code defines a function called
Person
that takesname
andage
as arguments. - Inside the function,
this.name = name;
andthis.age = age;
attach the name and age to the new object. -
person1
andperson2
are new objects created from thePerson
function. -
console.log(person1.name)
//Output: Alice -
console.log(person2.age)
//Output: 35
Closures and Private Members
- Using closures, private members can be created within constructor functions, enforcing data encapsulation and preventing direct access to sensitive information.
- Private data is typically held within a const or let that is enclosed in the constructor's scope.
- A getter function can be used to access private data, this prevents direct access.
Unique Identifier Function
- Closures and Immediately Invoked Function Expressions (IIFEs) can be used to create a unique identifier function.
- The function generates a unique id each time it's called
- The code maintains a counter within a closure that increments each time a unique id is needed.
Document Object Model (DOM)
- The DOM is a programming interface that makes it possible to access and manipulate HTML elements.
- The browser creates a hierarchical tree representation of the HTML document when the page loads.
- The components are called nodes.
DOM Node Types
- HTML elements, text, comments, are types of nodes.
- Each node has a
nodeType
property indicating its type.
Accessing DOM Elements
-
document.getElementById()
takes an element ID to find that element within the HTML document. -
document.getElementsByTagName()
takes a tag name to find all the elements with that tag. -
document.querySelector()
selects the first element matching a CSS selector. -
document.querySelectorAll()
selects all elements matching a CSS selector.
Additional DOM Selectors
- Class Selectors allow you to select elements with a given class.
- ID Selectors allows you to select elements based on their unique ID.
- Attribute Selectors let you choose elements with specific attributes.
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Description
This quiz covers the concept of closures in JavaScript, focusing on how functions defined within other functions can access their parent scope. You'll explore lexical scope and the practical use of closures with constructor functions. Test your understanding of these critical concepts in JavaScript development.