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What is hoisting in JavaScript?
Hoisting is a JavaScript mechanism where function declarations and variable declarations are moved to the top of their containing scope during compilation.
How are functions treated differently from variables in terms of hoisting?
Functions are fully hoisted, meaning their definitions are available before their actual location in the code, while variables declared with var are hoisted but initialized to undefined.
Why can you invoke a function before its definition in JavaScript?
You can invoke a function before its definition because the function's declaration is hoisted to the top of the global scope.
What happens to variables declared with let and const regarding hoisting?
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Are class declarations hoisted in JavaScript?
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What is the default value of variables hoisted with var?
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Can you give an example of a function being hoisted?
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How does hoisting affect scope in JavaScript?
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What is the difference between function and variable hoisting?
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What can occur if you try to use a let or const variable before it's declared?
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What is the main concept of hoisting in JavaScript?
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How does hoisting affect function declaration in JavaScript?
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Explain what happens when you try to call a function that is declared inside another function.
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In the given examples, why does calling printDillion()
result in a ReferenceError?
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What will the following code log: printHello(); function printHello() { console.log('hello'); }
?
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Is hoisting applicable to variable declarations in JavaScript? Explain.
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What do we mean by 'scope' in the context of hoisting?
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Compare hoisting in JavaScript with its presence in other programming languages.
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What is the outcome of console.log(x); var x = 5;
in JavaScript?
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Can let
and const
declarations be hoisted in JavaScript? How do they differ from var
?
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What is hoisting and how does it affect function declarations in JavaScript?
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How does hoisting behave differently for var
, let
, and const
in JavaScript?
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What happens when you try to access a let
variable before it is initialized?
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Explain the concept of the Temporal Dead Zone in relation to let
and const
.
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What error do you get when trying to log a const
variable before its initialization?
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Describe what happens when you try to access a variable declared within a function from outside that function.
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Can you access a function declared inside another function before its declaration? Why or why not?
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How does hoisting impact the initialization of variables declared with var
?
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What error occurs when you instantiate a class before its declaration, and why does this occur?
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Illustrate the difference in hoisting between a function declaration and a function expression.
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Study Notes
Hoisting in JavaScript
- Hoisting refers to the behavior where the declaration of functions, variables, and classes is moved to the top of their defined scope.
- This behavior is unique to JavaScript, differing from some other programming languages.
Function Hoisting
- Functions can be called before their declaration due to hoisting.
- Example: Calling
printHello()
returns "hello" even when declared afterwards. - Local scope functions (like
printDillion
insideprintHello
) are hoisted only within their own scope, leading to ReferenceErrors if called outside.
Variable Hoisting
- Hoisting applies to variables declared with
var
,let
, andconst
, but behaves differently for each. -
Var:
- Declaration is hoisted, defaulting to
undefined
. - Example:
var name; console.log(name);
outputsundefined
.
- Declaration is hoisted, defaulting to
-
Let:
- Declaration is hoisted but not initialized, resulting in a ReferenceError if accessed before the declaration.
- Example:
let name; console.log(name);
gives an error: "Cannot access 'name' before initialization."
-
Const:
- Similar to
let
, hoisted but inaccessible until initialized. - Example:
const name; console.log(name);
gives the same error aslet
.
- Similar to
Class Hoisting
- Classes are also hoisted but remain inaccessible until declared.
- Example: Instantiating a class before its declaration results in a ReferenceError.
- Classes, like
let
andconst
, are hoisted to top but not initialized.
Summary of Hoisting Behavior
- Functions maintain access to their logic and can be invoked before their declaration.
- Variables declared with
var
are hoisted with a default value ofundefined
. - Variables declared with
let
andconst
, as well as classes, are hoisted but cannot be accessed until they are initialized, leading to a "Temporal Dead Zone."
Practical Implications
- Understanding hoisting aids in effective troubleshooting and debugging in JavaScript code.
- Code functionality can remain intact even when function declarations are placed after their calls, due to hoisting.
- Developers must be cautious with variable declarations to avoid unexpected behavior.
Conclusion
- Hoisting is a fundamental concept in JavaScript that impacts how code is executed.
- It is crucial for developers to grasp hoisting to write clean, effective JavaScript code and avoid common pitfalls.
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Description
This quiz dives into the concept of hoisting in JavaScript, a vital behavior that determines how functions, variables, and classes operate within their scopes. Understanding hoisting is essential for mastering JavaScript, as it impacts how code is structured and executed. Test your knowledge and grasp this fundamental concept effectively.