lift parts out of a value using the Object constructor guard

lift-parts.js

// 17 February 2023
// lift parts out of a value
// using the Object constructor guard

function lift(v, key) {
  var o = Object(v);

  return Object.hasOwn(o, key)
    ? o[key]
    : undefined;
}

function parts(v, keys = []) {
  var p = {};

  ["valueOf", "toString"].concat(keys).forEach(function(key, _) {
    
    _ = lift(v, key);

    _ != null && (p[key] = _);
  });
    
  return p;
}

console.log(
lift(["hello, "])
);

console.log(
lift(["hello, "], 0) + "world"
);

console.log(
parts(["hello, "])[0]
);

console.log(
parts(["hello, "]).toString() + "world"
);

console.log(
parts(1, ['greet']).toString()
);

console.log(
parts({"greet": "hello, ", toString() { return this.greet; } }, ['greet']) + "world"
);

/*
undefined
hello, world
undefined
[object Object]world
[object Object]
hello, world
*/