How to convert nested JSON into flat object?

What is the most efficient way of converting in JavaScript object like:

const entries = {
  "name": "Mustang",
  "parts": {
    "tire": "example",
    "wheel": "example" 
  }
}

into flat object like:

const converted = {
  "name": "Mustang",
  "parts/tire": "example",
  "parts/wheel": "example"
}

no matter how many nested object inside.