JavaScript's lexical scope defines how variable names are resolved in nested functions. Variables declared in outer functions are accessible to functions defined within them, creating a scope chain that determines variable accessibility.

The scope chain follows these key principles:

• Inner functions can access variables from their outer scope
• Outer functions cannot access variables from inner scopes
• Variables with the same name take precedence in their local scope
• Global variables have the lowest precedence

Here's how lexical scoping works in practice:

const globalVar = "I'm global";

function outerFunction() {
    const outerVar = "I'm from outer";
    
    function innerFunction() {
        const innerVar = "I'm from inner";
        console.log(innerVar);     // Accessible
        console.log(outerVar);     // Accessible
        console.log(globalVar);    // Accessible
    }
    
    innerFunction();
    console.log(innerVar);         // Not accessible
}

Understanding lexical scope is crucial for:

• Avoiding naming conflicts
• Managing variable accessibility
• Writing maintainable code
• Implementing closures effectively
• Preventing unintended variable leaks

Best practices include:

• Using block scope with let and const
• Avoiding global variables when possible
• Keeping functions focused and small
• Understanding the scope chain hierarchy
• Leveraging closures intentionally

This scoping mechanism makes JavaScript code more predictable and helps prevent unintended variable access across different parts of an application.

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