When to use JavaScript const? Always declare a variable with const when you know that the value should not be changed. Use const when you declare: A new Array; A new Object; A new Function; A new RegExp

Mar 19, 2025 · The const declaration declares block-scoped local variables. The value of a constant can't be changed through reassignment using the assignment operator, but if a constant is an object, its properties can be added, updated, or removed.

Apr 2, 2020 · var variables can be updated and re-declared within its scope; let variables can be updated but not re-declared; const variables can neither be updated nor re-declared. They are all hoisted to the top of their scope.

Apr 7, 2025 · var: Declares variables with function or global scope and allows re-declaration and updates within the same scope. let: Declares variables with block scope, allowing updates but not re-declaration within the same block. const: Declares block-scoped variables that cannot be reassigned after their initial assignment. 1. Declaring Variables with var.

Jan 20, 2014 · const creates an immutable binding, meaning a const variable identifier is not reassignable. const a = "value1"; You cannot reassign it with. a = "value2"; However, if the const identifier holds an object or an array, the value of it can …

Sep 25, 2008 · Since ES2015, JavaScript has a notion of const: This will work in pretty much all browsers except IE 8, 9 and 10. Some may also need strict mode enabled. You can use var with conventions like ALL_CAPS to show that certain values should not be modified if you need to support older browsers or are working with legacy code:

So the usual rules around variable hoisting within a scope -- block-scoped variables (let and const) do not hoist as undefined to the top of their block scope. This means: doSomething() // will fail.

Feb 12, 2025 · The const keyword in JavaScript is a modern way to declare variables, introduced in (ES6). It is used to declare variables whose values need to remain constant throughout the lifetime of the application. const is block-scoped, similar to let, and is useful for ensuring immutability in your code.

Mar 18, 2025 · When learning JavaScript, understanding the difference between let, var, and const is essential. These three keywords are used for variable declaration, but they behave differently. Using them correctly can improve the efficiency, maintainability, and security of …

Jan 11, 2023 · var and let create variables that can be reassigned another value. const creates "constant" variables that cannot be reassigned another value. developers shouldn't use var anymore. They should use let or const instead. The first two points are likely pretty self-explanatory. But what about why we shouldn't use var, or when to use let vs const?