For TypeScript, under what circumstances would you choose to use "let" versus "const"?
For TypeScript, under what circumstances would you choose to use "let" versus "const"?
const represents a constant, indicating that the variable cannot be changed at a later time.
let is similar to var but is limited to block scope, allowing it to be declared within a for loop and only accessible within that loop's body.
This differs from a var variable, which can be declared anywhere but remains local to the function scope.
It is advisable to use const for defining variables whenever possible as a best practice.
Since I primarily engage in functional programming, I often see little use for distinguishing between const and let. I have a strict practice of never reassigning values to variables, regardless of the programming language.
However, there are some issues with the conventional usage of these declarations that I find troubling:
const is longer than let, which may seem trivial but can be an inconvenience.const somewhat implies permanence, leading to confusion among colleagues who may expect the value to never change.Consider this example:
const x = { foo: "bar" }
x["foo"] = "Not bar!"
Although the variable name and its reference remain constant, the object being referenced is mutable. This discrepancy becomes clearer when working with Typescript, where you can define readonly types:
type ROO = Readonly<SomeType>
const x: ROO = someReferenceValue
x.someProp = "A wanna be a bar!" //compile error
In the context of Typescript, using const finally truly represents constancy.
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