bar-2.js

function f(a) {
  if (a > 1000) return 1
  if (a > 100)  return 2
  if (a > 10)   return 3
  return 4
}

var i = 100000;
while (i--) {
  f(Math.random() * 1000)
}

// $ node --trace-inlining bar-2.js 
// Inlining builtin 0x148b0391c829 <JS Function random>
// Inlined f called from .

bar.js

function f(a) {
  if (a > 1000) return 1
  if (a > 100)  return 2
  if (a > 10)   return 3
  return f
}

var i = 100000;
while (i--) {
  f(Math.random() * 1000)
}

// $ node --trace-inlining bar.js 
// Inlining builtin 0x31104761c829 <JS Function random>
// Did not inline f called from  (target requires context change).

(It apparently does inline if the inconsistent types are primitives/nullables, though)