y-example-7.js

// original
const Y = f => (x => f(v => x(x)(v)))(x => f(v => x(x)(v)))

// expanded as
const Y = f => {
  // return the result of this IIFE
  // f produces the fixed point function
  return (x => {
    // outer:
    f(v => {
      // invoke inner x with x as arg, 
      // returns fixed point which takes v
      // f is invoked only once on this side
      return x(x)(v)
    })
  })(x => {
    // inner:
    f(v => {
      // invoke inner x with x as arg,
      // returns fixed point which takes v
      // this f is invoked every subsequent time
      return x(x)(v)
    })
  })
}

Refer to The Mysterious Y-combinator