var vs let vs const
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Understanding the Difference Between var, let, and const in JavaScript (25 views)
11 Mar 2025 16:47
<table id="boardTable" class="section-table" style="border-collapse: collapse; border: 1px solid silver; font-family: arial;" border="1" width="100%" cellspacing="0" cellpadding="6">
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<td style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; font-size: 13px; line-height: normal; font-family: arial; border-collapse: collapse; border: 1px solid silver;" valign="top" width="100%">Introduction to JavaScript Variables
JavaScript provides three ways to declare variables: var, let, and const. While var was used in older JavaScript versions, let and const were introduced in ES6 to improve variable handling and avoid common issues related to scope and reassignment var vs let vs const.
Scope Differences: Global vs. Block Scope
The var keyword has function scope, meaning it is accessible throughout the function in which it is declared. On the other hand, let and const have block scope, meaning they are only accessible within the block {} in which they are defined. This makes let and const safer to use in modern JavaScript.
Hoisting Behavior in var, let, and const
All three declarations are hoisted, but var is initialized as undefined, allowing access before the actual declaration. However, let and const remain in the temporal dead zone (TDZ) until their declaration is executed, preventing accidental access before initialization.
Reassignment and Mutability
Variables declared with var and let can be reassigned, but const prevents reassignment after initialization. However, objects and arrays declared with const can still have their properties or elements modified, though the reference itself cannot change.
Best Practices for Choosing Between var, let, and const
Use const by default to ensure values do not change.
Use let only when reassignment is necessary.
Avoid var as it can lead to scope-related bugs and unintended reassignments.
Conclusion: let and const for Modern JavaScript
With ES6 improvements, let and const have replaced var for better variable management. Using const whenever possible ensures more stable and predictable code, while let provides flexibility for reassignment. Understanding these differences helps write cleaner and more efficient JavaScript code.
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var vs let vs const
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