thunk

 In computer programming, a thunk is a subroutine used to inject a calculation into another subroutine. Thunks are primarily used to delay a calculation until its result is needed, or to insert operations at the beginning or end of the other subroutine. They have many other applications in compiler code generation and modular programming

 

// 'hypot' is a binary function
const hypot = (x, y) => Math.sqrt(x * x + y * y);

// 'thunk' is a function that takes no arguments and, when invoked, performs a potentially expensive
// operation (computing a square root, in this example) and/or causes some side-effect to occur
const thunk = () => hypot(3, 4);

// the thunk can then be passed around without being evaluated...
doSomethingWithThunk(thunk);

// ...or evaluated
thunk(); // === 5