Conditionally initializing a constant in Javascript

Question

ES6 onwards we have const.

This is not allowed:

const x; //declare first //and then initialize it if(condition) x = 5; else x = 10; 

This makes sense because it prevents us from using the constant before it's initialized.

But if I do

if(condition)     const x = 5;  else      const x = 10; 

x becomes block scoped.

So how to conditionally create a constant?

Answer 1

Your problem, as you know, is that a const has to be intialised in the same expression that it was declared in.

This doesn't mean that the value you assign to your constant has to be a literal value. It could be any valid expression really - ternary:

const x = IsSomeValueTrue() ? 1 : 2; 

Or maybe just assign it to the value of a variable?

let y = 1; if(IsSomeValueTrue()) {     y = 2; }  const x = y; 

You could of course assign it to the return value of a function, too:

function getConstantValue() {     return 3; }  const x = getConstantValue(); 

So there's plenty of ways to make the value dynamic, you just have to make sure it's only assigned in one place.