Function assignValue

lib/utils.js:463–485

(val, key)

  const { caseless, skipUndefined } = (isContextDefined(this) && this) || {};
  const result = {};
  const assignValue = (val, key) => {
    // Skip dangerous property names to prevent prototype pollution
    if (key === '__proto__' || key === 'constructor' || key === 'prototype') {
      return;
    }

    // findKey lowercases the key, so caseless lookup only applies to strings —
    // symbol keys are identity-matched.
    const targetKey = (caseless && typeof key === 'string' && findKey(result, key)) || key;
    // Read via own-prop only — a bare `result[targetKey]` walks the prototype
    // chain, so a polluted Object.prototype value could surface here and get
    // copied into the merged result.
    const existing = hasOwnProperty(result, targetKey) ? result[targetKey] : undefined;
    if (isPlainObject(existing) && isPlainObject(val)) {
      result[targetKey] = merge(existing, val);
    } else if (isPlainObject(val)) {
      result[targetKey] = merge({}, val);
    } else if (isArray(val)) {
      result[targetKey] = val.slice();
    } else if (!skipUndefined || !isUndefined(val)) {
      result[targetKey] = val;
    }
  };

  for (let i = 0, l = objs.length; i < l; i++) {
    const source = objs[i];