JavaScript Basics & Syntax Quiz

Lexical Scope

Lexical Scope: Where Code is Written Matters

Lexical scope means that where you write your code determines what variables you can access. It’s like a family tree – children can access their parents’ things, but parents can’t access their children’s things.

Basic Lexical Scope

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Scope Chain

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Variable Shadowing

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Practical Examples

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// Configuration object with nested access
let config = {
  api: {
    baseUrl: 'https://api.example.com',
    timeout: 5000,
    headers: {
      'Content-Type': 'application/json',
      'Authorization': 'Bearer token123'
    }
  },
  database: {
    host: 'localhost',
    port: 5432,
    name: 'myapp'
  }
};

function makeApiCall(endpoint) {
  // Can access config.api from this scope
  let url = config.api.baseUrl + endpoint;
  let timeout = config.api.timeout;
  
  console.log('Making request to: ' + url);
  console.log('Timeout: ' + timeout + 'ms');
}

makeApiCall('/users');

// Module pattern using lexical scope
let calculator = (function() {
  // Private variables (only accessible within this function)
  let history = [];
  let operationCount = 0;
  
  // Private function
  function logOperation(operation, result) {
    history.push({
      operation: operation,
      result: result,
      timestamp: new Date()
    });
    operationCount++;
  }
  
  // Public interface (returned object)
  return {
    add: function(a, b) {
      let result = a + b;
      logOperation('add', result); // Can access private function
      return result;
    },
    getHistory: function() {
      return history; // Can access private variable
    },
    getCount: function() {
      return operationCount; // Can access private variable
    }
  };
})();

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

Common Mistakes

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Tip: Remember that JavaScript looks for variables from the current scope outward, and inner scopes can access outer scopes but not vice versa!