034.2 JavaScript Data Structures (weight: 3) WEB-DEVELOPMENT-ESSENTIALS Practice Questions (Page 4)

Questions 16–20

1. 16foundation · easy

   What is the value of x after the following code runs? console.log(x); var x = 5;

   • Aundefined
   • B5
   • Cnull
   • DReferenceError
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2. 17foundation · easy

   Which type of scope does a variable declared with var inside a function have?

   • ABlock scope
   • BModule scope
   • CGlobal scope
   • DFunction scope
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4. 18foundation · easy

   What happens when you attempt to reassign a variable declared with const?

   • AThe variable is automatically converted to let.
   • BA TypeError is thrown.
   • CThe new value is assigned but the variable becomes immutable.
   • DThe reassignment silently fails and the original value remains.
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5. 19foundation · easy

   A variable declared with let inside an if block is accessible where?

   • AThroughout the entire function
   • BGlobally
   • COnly inside that if block
   • DOnly inside the if block and its parent block
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6. 20application · medium

   A developer needs to store a list of user IDs and then quickly check if a specific ID exists. The list will be modified frequently. Which data structure is most appropriate, and why?

   • AA string, because it is a primitive type that can store a comma-separated list.
   • BAn object, because it is a complex data type that allows key-value storage.
   • CA Set, because it is a complex data type that provides O(1) average-time membership checks.
   • DAn array, because it is a complex data type that supports direct indexing and iteration.
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