variables.md

Variables

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List

1. Don't use 'var'
2. Scope
3. Global Scope
4. Temporary Variables
5. Hoisting

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Don't use 'var'

Using let and const instead of var helps avoid issues with scope and hoisting.

// Bad
var count = 1;

// Good
let count = 1;
const MAX_COUNT = 10;

Scope

Understanding variable scope is essential for writing predictable and bug-free code.

function example() {
  let localVariable = 'I am local';
  if (true) {
    let blockScoped = 'I am block scoped';
    console.log(blockScoped); // Output: I am block scoped
  }
  console.log(localVariable); // Output: I am local
  // console.log(blockScoped); // Error: blockScoped is not defined
}

example();

Global Scope

Minimize the use of global variables to avoid conflicts and unexpected behavior.

// Bad: Global variable
var globalCount = 0;

// Good: Encapsulated variable
function incrementCount() {
  let count = 0;
  count++;
  return count;
}

incrementCount(); // 1
incrementCount(); // 1 (no conflict with previous call)

Temporary Variables

Use descriptive names for temporary variables and avoid unnecessary ones.

// Bad: Global variable
var globalCount = 0;

// Good: Encapsulated variable
function incrementCount() {
  let count = 0;
  count++;
  return count;
}

incrementCount(); // 1
incrementCount(); // 1 (no conflict with previous call)

Hoisting

Hoisting is JavaScript’s behavior of moving declarations to the top of their scope. Understanding hoisting helps prevent bugs.

// Bad
console.log(hoistedVar); // Output: undefined
var hoistedVar = 'This is hoisted';

// Good
let notHoistedVar;
console.log(notHoistedVar); // Output: undefined
notHoistedVar = 'This is not hoisted';