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Questions and Answers
What keyword is used to define variables that can change their values in JavaScript?
Which type of variable scope applies to curly bracket blocks in JavaScript?
What process does JavaScript perform with the var keyword to lift variable declarations to the top of their scope?
Which type of scope pertains to named functions and arrow functions in JavaScript?
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In JavaScript, which keyword is used for variables that remain constant throughout the program?
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What error occurs in JavaScript when attempting to use a variable without initializing it?
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Study Notes
Variables in JavaScript
Variables in JavaScript are containers that hold values. They begin with let or const, depending on whether they will change or remain constant throughout the program. Here's how to define a variable:
let myVarName = 'exampleValue';
After defining a variable, you can assign new values to it later using =. For instance:
myVarName = 'newExampleValue';
There are several types of variables, including strings, booleans, integers, floating points, null, undefined, and symbols. Each type plays a role in the dynamic nature of JavaScript, allowing the engine to interpret expressions based on the context.
Scope
In JavaScript, variables can either have a block scope or function scope. Block scope applies to curly bracket blocks ({}) while function scope pertains to named functions and arrow functions. Block scope variables exist until the end of the block, whereas function scope variables persist after the function returns its result.
Hoisting
With the var keyword, JavaScript performs a process known as hoisting. Variable declarations are lifted to the top of their scope, making it valid to reference a variable before its declaration. However, hoisting attaches a variable to the current scope only upon assignment to it. Hence, attempting to use a variable without initializing it will cause a Reference Error.
Shadowing
Shadowing occurs when a higher scope variable shares the same name as a lower scope variable. In this case, the higher scope variable takes precedence. Lower scope variables cannot shadow higher scope ones because they are treated as distinct entities even though they share names.
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Description
Test your knowledge of JavaScript variables, including how to define and assign them, different variable types, and the concept of scope. Learn about hoisting and how it affects variable declarations, and understand the concept of shadowing in JavaScript.
