JavaScript Basics & Syntax Quiz

Scopes

Scopes: Where Variables Live

Scope determines where variables are accessible in your code. Think of it like rooms in a house – some things are available everywhere, others only in specific rooms.

Global Scope – Available Everywhere

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Function Scope – Variables Inside Functions

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Block Scope – Variables Inside Blocks

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var vs let/const Scope

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Nested Scopes - Scope Chain

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Practical Examples

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// Module pattern using scope
let calculator = (function() {
  // Private variables (function scope)
  let history = [];
  let operationCount = 0;
  
  // Private functions
  function addToHistory(operation, result) {
    history.push({ operation: operation, result: result, timestamp: new Date() });
    operationCount++;
  }
  
  // Public interface
  return {
    add: function(a, b) {
      let result = a + b;
      addToHistory('add', result);
      return result;
    },
    getHistory: function() {
      return history;
    },
    getOperationCount: function() {
      return operationCount;
    }
  };
})();

console.log(calculator.add(5, 3)); // 8
console.log(calculator.getOperationCount()); // 1
// console.log(calculator.history); // undefined (private)

// Block scope in loops
let buttons = ['Button 1', 'Button 2', 'Button 3'];

for (let i = 0; i < buttons.length; i++) {
  // Each iteration has its own i variable
  setTimeout(function() {
    console.log('Clicked: ' + buttons[i]);
  }, i * 1000);
}
// This works correctly because each iteration has its own i

Best Practices

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Tip: Use const and let instead of var to avoid scope confusion!