Questions and Answers
What is the main purpose of a function in JavaScript?
What is a closure in JavaScript?
Which of the following function types is not hoisted?
How do you define default parameters in a function?
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Which of the following is an example of a higher-order function?
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What will a function return if no return statement is specified?
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In which scope are variables declared inside a function accessible?
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What distinguishes an IIFE from regular functions?
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Which statement about Arrow Functions is correct?
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What does the return keyword do in a function?
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Study Notes
Overview of Functions in JavaScript
- Definition: Functions are reusable blocks of code that perform a specific task.
Types of Functions
-
Function Declarations
- Syntax:
function functionName(parameters) { // code to be executed } - Hoisted: Can be called before their definition in the code.
- Syntax:
-
Function Expressions
- Syntax:
const functionName = function(parameters) { // code to be executed }; - Not hoisted: Must be defined before calling.
- Syntax:
-
Arrow Functions
- Syntax:
const functionName = (parameters) => { // code to be executed }; - Shorter syntax and does not bind its own
this.
- Syntax:
Parameters and Arguments
- Parameters: Variables listed in the function’s definition.
- Arguments: Values passed to the function when it is called.
- Default parameters can be set using:
function functionName(param1 = defaultValue) { // code }
Return Statement
- Use the
returnkeyword to send a value back to the caller. - If no return is specified, the function returns
undefined.
Scope
- Functions create their own scope:
- Local Scope: Variables declared inside a function are not accessible outside.
- Global Scope: Variables declared outside any function are accessible throughout the program.
Higher-order Functions
- Functions that take other functions as arguments or return them.
- Commonly used in array methods like
map,filter, andreduce.
IIFE (Immediately Invoked Function Expression)
- A function that runs as soon as it is defined.
- Syntax:
(function() { // code to be executed })();
Closures
- A function that retains access to its lexical scope, even when the function is executed outside that scope.
- Useful for data encapsulation and private variables.
Callback Functions
- Functions passed as arguments to other functions, invoked after some operation is completed.
- Common in asynchronous programming.
Function Methods
-
call(): Invokes a function with a specified
thisvalue and arguments. -
apply(): Similar to
call(), but takes an array of arguments. -
bind(): Returns a new function, permanently bound to a specific
thisvalue.
Recursion
- A function that calls itself either directly or indirectly.
- Must have a base case to avoid infinite loops.
Best Practices
- Use descriptive names for functions.
- Keep functions small and focused on a single task.
- Document functions with comments for better understanding.
Overview of Functions in JavaScript
- Functions are reusable blocks of code designed to perform specific tasks.
Types of Functions
-
Function Declarations: Defined with the
functionkeyword and are hoisted, allowing them to be called before their definition. - Function Expressions: Assigned to variables and must be defined before being called; they are not hoisted.
-
Arrow Functions: Introduced with a concise syntax; they do not bind their own
this, making them useful in certain contexts.
Parameters and Arguments
- Parameters: Variables defined in a function's declaration.
- Arguments: Actual values passed to a function when it is called.
- Default parameters can be established to provide fallback values.
Return Statement
- The
returnkeyword is used to send a value back to the caller; absence of return results inundefined.
Scope
- Functions generate unique scopes:
- Local Scope: Variables defined inside a function are not accessible outside.
- Global Scope: Variables defined outside functions are accessible throughout the program.
Higher-order Functions
- Functions that accept other functions as arguments or return them.
- Commonly utilized in array methods such as
map,filter, andreduce.
IIFE (Immediately Invoked Function Expression)
- A function that executes immediately upon definition.
- Noted for its syntax, which includes wrapping the function expression in parentheses followed by parentheses.
Closures
- Functions that maintain access to their lexical scope, even when executed outside of that scope.
- Effective for data encapsulation and managing private variables.
Callback Functions
- Functions provided as arguments to other functions, executed after the completion of an operation.
- Frequently used in asynchronous programming to handle events after completion.
Function Methods
-
call(): Calls a function with a specified
thisvalue and individual arguments. -
apply(): Similar to
call(), but takes arguments as an array. -
bind(): Creates a new function that is permanently bound to a specified
thisvalue.
Recursion
- A technique where a function calls itself either directly or indirectly.
- Requires a base case to prevent infinite looping.
Best Practices
- Opt for descriptive function names for clarity.
- Keep functions concise and focused on a single responsibility.
- Document functions with comments to enhance understanding.
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Description
This quiz covers the fundamentals of functions in JavaScript, including their definitions, types, and the differences between declarations and expressions. It also discusses parameters and arguments, providing a clear understanding of how functions operate within the language.
