I know this question title looks scary, but it isn't. Sorry!
Ok, so, what's the point of creating a one-time-only/unchangeable "variable"?
Lets say I have one property called "name" in a Person object.
const Person = {
name: 'Luis Felipe Zaguini'
};
Alright. So, it's incredibly common to see people doing this:
let personName = Person.name;
console.log(`I've written my name, and it is ${personName}.`);
And that's it. In the majority of times that variable is used only once. Or, sometimes, it's referenced in other statements, but you know, it's useless because there IS a way to reference it without setting a new variable.
Tecnically, you're wasting CPU memory, allocating memory for something useless because you can, in fact, type Person.name multiple times, and do this:
console.log(`I've written my name, and it is ${Person.name}.`);
Also, you're wasting time and adding more lines to your code. Am I overracting? Lot of programmers do this kind of stuff, but personally it doesn't seem to fit very well to me.
There are any number of reasons
A 'const` variable will prevent the value from accidentally changing, e.g. if you have written a closure that includes a variable that is accessible outside immediate scope.
Javascript engines are not yet capable of common subexpression elimination, which is a very common compiler optimization. Using a temporary variable could improve performance, like in this example.
Sometimes a variable with a different name can clarify the functionality; see Writing Really Obvious Code (ROC). Example:
var activeUsername = User.name; //It's not just a user's name, it's the active user's name!
Sometimes that extra variable makes it easier to debug/watch variables
Sometimes you want to set a separate breakpoint during the assignment
Am I overracting?
Yes.