Optional API javascript

optional.js

function optionalAccess(obj, path, def) {
  const propNames = path.replace(/\]|\)/, "").split(/\.|\[|\(/);

  return propNames.reduce((acc, prop) => acc[prop] || def, obj);
}

function proxyOptional(obj, evalFunc, def) {
  const handler = {
    get: function(target, prop, receiver) {
      const res = Reflect.get(...arguments);
      return typeof res === "object" ? proxify(res) : res != null ? res : def;
    }
  };

  const proxify = target => {
    return new Proxy(target, handler);
  };

  return evalFunc(proxify(obj, handler));
}

const obj = {
  items: [{ hello: "Hello" }]
};

console.log(optionalAccess(obj, "items[0].hello", "def")); // Prints Hello
console.log(optionalAccess(obj, "items[0].he", "def")); // Prints def

console.log(proxyOptional(obj, target => target.items[0].hello, "def")); // Prints Hello
console.log(proxyOptional(obj, target => target.items[0].hell, { a: 1 })); // Prinst { a: 1 }

console.log((obj && obj.items && obj.items[0] && obj.items[0].hello) || "def"); // Prints Hello
console.log((obj && obj.items && obj.items[0] && obj.items[0].hel) || "def"); // Prints def

Nice. The proxyOptional function can also work well as Object.prototype:

Object.prototype.optional = function (evalFunc, def) {
    const handler = {
        get: function(target, prop, receiver) {
        const res = Reflect.get(...arguments);
        return typeof res === "object" ? proxify(res) : res != null ? res : def;
        }
    }

    const proxify = target => {
        return new Proxy(target, handler);
    }

    return evalFunc(proxify(this, handler));
}


// Example
const greeting = {
    items: [{ hello: undefined}],
}
 
result = greeting.optional(obj => obj.items[0].hello, null)
console.log(result) // prints null