Var

What is the var keyword and why is it no longer suggested to use it?

The var keyword in JavaScript is one of the original ways to declare variables. It has been part of the language since its inception and for many years it remained the primary method for creating variables. However as JavaScript evolved and developers gained more experience with the language, certain drawbacks of using var became apparent leading to the introduction of let and const in 2015.

When you declare a variable with var, it becomes function-scoped or globally-scoped. This means that if you declare a variable inside a function using var it’s only accessible within that function. However if you declare it outside any function, it becomes a global variable accessible throughout your entire script. This behavior can sometimes lead to unexpected results and make your code harder to reason about.

A problem with var is that it allows you to redeclare the same variable multiple times without throwing an error. This can lead to accidental overwrites and make debugging more difficult.

var num = 5;
 
// This is allowed and doesn't throw an error
var num = 10;

The most significant issue with var is its lack of block scoping. Variables declared with var inside a block like an if statement or a for loop are still accessible outside that block.

if (true){
  var num = 5;
}
console.log(num); // 5

This behaviour can lead to unintended variable leaks and make your code more prone to bugs.

Due to this issues, modern JavaScript development has largely moved away from var in favor of let and const. These keywords provide block scoping which aligns more closely with how scoping works in many other programming languages.

They also don’t allow redeclaration within the same scope helping to prevent accidental overrides.

While var is still part of JavaScript and works in all browsers, it’s generally recommended to use let and const in modern JavaScript development. They provide clear scoping rules help prevent common pitfalls and make your code’s behavior more predictable.

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