rAssign library, slightly refactored; see https://github.com/micnic/r-assign/

rAssign-refactored.js

// 21 February 2021
// rAssign library, slightly refactored

// r-assign by micnic applies Object.assign() to a series of sources,
// then uses a schema against which to extract defined properties by type and name.
// see https://github.com/micnic/r-assign/

function rAssign(schema, ...sources) {

  // Check for valid schema provided
  if (!schema || typeof schema !== 'object') {
    throw TypeError(invalidSchema);
  }

  var source = Object.assign({}, ...sources);

  // Loop through schema properties to select them
  return Object.keys(schema).reduce((result, key) => {

    // Check for valid schema properties
    if (typeof schema[key] !== 'function') {
        throw TypeError(invalidSchemaProperty(key));
    }

    var value = schema[key](source[key], key, source);

    // Skip values that are undefined
    if (typeof value !== 'undefined') {
        result[key] = value;
    }

    return result;
  }, {})
};

var invalidSchema = 'Invalid schema argument type, object expected';

/**
 * Returns message for invalid schema property error
 * @param {string} key
 * @returns {string}
 */
function invalidSchemaProperty(key) {
  return `Invalid property type, "${key}" property expected to be a function`;
};



/* full entry test */

function getNumber(value){
  return typeof value === 'number'
    ? value
    : 0
};

function getString(value){
  return typeof value === 'string'
    ? value
    : ""
};

var fullEntry = {
  id: '5cdb44a49539f8cd',
  index: 0,
  visible: true,
  name: 'abc'
};

var F = rAssign({
  id: getString,
  index: getNumber,
  name: getString
}, fullEntry);

console.log(F)
// {id: "5cdb44a49539f8cd", index: 0, name: "abc"}

/* partial test */

function getBoolean(value) {
  return typeof value === 'boolean'
    ? value
    : false
};

var partialEntry = {
  id: 'da9c8dff96b060a9',
  index: 1,
  name: 'def'
};

var P = rAssign({
  id: getString,
  visible: getBoolean,
  name: getString
}, fullEntry, partialEntry);

console.log(P)
// {id: "da9c8dff96b060a9", visible: true, name: "def"}

/* invalid entry test */

function validateNumber(value) {
  if (typeof value !== 'number') {
    throw new Error(`Value "${value}" expected to be a number`);
  }

  return value;
};

var invalidEntry = {
  id: '8a4eebf45748c8a4',
  index: false,
  name: 'ghi'
};

try {
  var I = rAssign({
    id: getString,
    index: validateNumber,
    visible: getBoolean,
    name: getString
  }, invalidEntry);
} catch(error) {
  console.error(error)
  // Uncaught Error: Value expected to be a number
}

/*
  Empty schema: returns empty object.

  This is contrary behavior to schema-ensure which requires the defined properties to exist while accepting any others.
  See https://gist.github.com/dfkaye/5799d75d8190246a32613ea6e86e3be4
 */

var E = rAssign({}, fullEntry);

console.log(E)
// {}