Proper terminology for replacing myValue with myValue()

Question

I keep seeing this pattern of value replacement, and I'm trying to figure out how I can explain the substitution to my coworkers.

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Question

What are the proper, definitive words for:

1. this substitution
2. the substituted function

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In many applications, you need to re-query the value rather than use an existing, defined variable.

Advanced use-cases:

1. trampolining
2. using functions as React children, rather than JSX / HTML

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Example Animation

const initialValue = (
  +(0.5 * window.innerHeight)
);

const remainingValue = (
  -(initialValue)
  +(0.25 * window.innerHeight)
);

function getTopValue (percentageComplete) {
  return (
    +(initialValue)
    +(percentageComplete * remainingValue)
  );
}

If you were to call getTopValue over a few seconds with values between 0 and 1, you eventually end up at initial + remaining

However, if you are to resize the screen, your end destination is different, and you must turn remainingValue into a function, rather than a value

const initialValue = (
  +(0.5 * window.innerHeight)
);

const remainingValue = () => (
  -(initialValue)
  +(0.25 * window.innerHeight)
);

function getTopValue (percentageComplete) {
  return (
    +(initialValue)
    +(percentageComplete * remainingValue())
  );
}

Answer 1

1. lazy evaluation -- strategy which delays the evaluation of an expression until its value is needed
2. thunk -- a parameterless closure created to prevent the evaluation of an expression until forced at a later time