Creating and finding posts using Parse.com
This depends on the scope in which you want the variable to have.

Is the variable the same between the two function calls? if so, you would tend to only define it once, as calling it twice may be expensive.

Interestingly however, you've defined an ES6 const which will complain if you redefine the same value (which is why I presume you've named the variable differently). 

If you intended the variable to be different between the two calls, you would normally not use const.

Looking at your example, I would define this variable once, and use the const keyword in order to explicitly avoid is being redefined by accident elsewhere. 

You also ask about conventions. Looking at the MDN page for const, they advise naming constants with uppercase characters. So I would probably go down that route unless it contravenes your coding style: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const