Fix merging with empty values

.gitignore

@@ -1,2 +1 @@
 node_modules
-dist/*

dist/cjs.js

@@ -0,0 +1,139 @@
+'use strict';
+
+var isMergeableObject = function isMergeableObject(value) {
+	return isNonNullObject(value)
+		&& !isSpecial(value)
+};
+
+function isNonNullObject(value) {
+	return !!value && typeof value === 'object'
+}
+
+function isSpecial(value) {
+	var stringValue = Object.prototype.toString.call(value);
+
+	return stringValue === '[object RegExp]'
+		|| stringValue === '[object Date]'
+		|| isReactElement(value)
+}
+
+// see https://github.com/facebook/react/blob/b5ac963fb791d1298e7f396236383bc955f916c1/src/isomorphic/classic/element/ReactElement.js#L21-L25
+var canUseSymbol = typeof Symbol === 'function' && Symbol.for;
+var REACT_ELEMENT_TYPE = canUseSymbol ? Symbol.for('react.element') : 0xeac7;
+
+function isReactElement(value) {
+	return value.$$typeof === REACT_ELEMENT_TYPE
+}
+
+function emptyTarget(val) {
+	return Array.isArray(val) ? [] : {}
+}
+
+function cloneUnlessOtherwiseSpecified(value, options) {
+	return (options.clone !== false && options.isMergeableObject(value))
+		? deepmerge(emptyTarget(value), value, options)
+		: value
+}
+
+function defaultArrayMerge(target, source, options) {
+	return target.concat(source).map(function(element) {
+		return cloneUnlessOtherwiseSpecified(element, options)
+	})
+}
+
+function getMergeFunction(key, options) {
+	if (!options.customMerge) {
+		return deepmerge
+	}
+	var customMerge = options.customMerge(key);
+	return typeof customMerge === 'function' ? customMerge : deepmerge
+}
+
+function getEnumerableOwnPropertySymbols(target) {
+	return Object.getOwnPropertySymbols
+		? Object.getOwnPropertySymbols(target).filter(function(symbol) {
+			return target.propertyIsEnumerable(symbol)
+		})
+		: []
+}
+
+function getKeys(target) {
+	return Object.keys(target).concat(getEnumerableOwnPropertySymbols(target))
+}
+
+function propertyIsOnObject(object, property) {
+	try {
+		return property in object
+	} catch(_) {
+		return false
+	}
+}
+
+// Protects from prototype poisoning and unexpected merging up the prototype chain.
+function propertyIsUnsafe(target, key) {
+	return propertyIsOnObject(target, key) // Properties are safe to merge if they don't exist in the target yet,
+		&& !(Object.hasOwnProperty.call(target, key) // unsafe if they exist up the prototype chain,
+			&& Object.propertyIsEnumerable.call(target, key)) // and also unsafe if they're nonenumerable.
+}
+
+function mergeObject(target, source, options) {
+	var destination = {};
+	if (options.isMergeableObject(target)) {
+		getKeys(target).forEach(function(key) {
+			destination[key] = cloneUnlessOtherwiseSpecified(target[key], options);
+		});
+	}
+	getKeys(source).forEach(function(key) {
+		if (propertyIsUnsafe(target, key)) {
+			return
+		}
+
+		if (propertyIsOnObject(target, key)) {
+			if (options.isEmpty && options.isEmpty(source[key])) {
+				destination[key] = cloneUnlessOtherwiseSpecified(target[key], options);
+			} else if (options.isMergeableObject(source[key])) {
+				destination[key] = getMergeFunction(key, options)(target[key], source[key], options);
+			} else {
+				destination[key] = cloneUnlessOtherwiseSpecified(source[key], options);
+			}
+		} else {
+			destination[key] = cloneUnlessOtherwiseSpecified(source[key], options);
+		}
+	});
+	return destination
+}
+
+function deepmerge(target, source, options) {
+	options = options || {};
+	options.arrayMerge = options.arrayMerge || defaultArrayMerge;
+	options.isMergeableObject = options.isMergeableObject || isMergeableObject;
+	// cloneUnlessOtherwiseSpecified is added to `options` so that custom arrayMerge()
+	// implementations can use it. The caller may not replace it.
+	options.cloneUnlessOtherwiseSpecified = cloneUnlessOtherwiseSpecified;
+
+	var sourceIsArray = Array.isArray(source);
+	var targetIsArray = Array.isArray(target);
+	var sourceAndTargetTypesMatch = sourceIsArray === targetIsArray;
+
+	if (!sourceAndTargetTypesMatch) {
+		return cloneUnlessOtherwiseSpecified(source, options)
+	} else if (sourceIsArray) {
+		return options.arrayMerge(target, source, options)
+	} else {
+		return mergeObject(target, source, options)
+	}
+}
+
+deepmerge.all = function deepmergeAll(array, options) {
+	if (!Array.isArray(array)) {
+		throw new Error('first argument should be an array')
+	}
+
+	return array.reduce(function(prev, next) {
+		return deepmerge(prev, next, options)
+	}, {})
+};
+
+var deepmerge_1 = deepmerge;
+
+module.exports = deepmerge_1;

dist/umd.js

@@ -0,0 +1,145 @@
+(function (global, factory) {
+	typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
+	typeof define === 'function' && define.amd ? define(factory) :
+	(global = global || self, global.deepmerge = factory());
+}(this, (function () { 'use strict';
+
+	var isMergeableObject = function isMergeableObject(value) {
+		return isNonNullObject(value)
+			&& !isSpecial(value)
+	};
+
+	function isNonNullObject(value) {
+		return !!value && typeof value === 'object'
+	}
+
+	function isSpecial(value) {
+		var stringValue = Object.prototype.toString.call(value);
+
+		return stringValue === '[object RegExp]'
+			|| stringValue === '[object Date]'
+			|| isReactElement(value)
+	}
+
+	// see https://github.com/facebook/react/blob/b5ac963fb791d1298e7f396236383bc955f916c1/src/isomorphic/classic/element/ReactElement.js#L21-L25
+	var canUseSymbol = typeof Symbol === 'function' && Symbol.for;
+	var REACT_ELEMENT_TYPE = canUseSymbol ? Symbol.for('react.element') : 0xeac7;
+
+	function isReactElement(value) {
+		return value.$$typeof === REACT_ELEMENT_TYPE
+	}
+
+	function emptyTarget(val) {
+		return Array.isArray(val) ? [] : {}
+	}
+
+	function cloneUnlessOtherwiseSpecified(value, options) {
+		return (options.clone !== false && options.isMergeableObject(value))
+			? deepmerge(emptyTarget(value), value, options)
+			: value
+	}
+
+	function defaultArrayMerge(target, source, options) {
+		return target.concat(source).map(function(element) {
+			return cloneUnlessOtherwiseSpecified(element, options)
+		})
+	}
+
+	function getMergeFunction(key, options) {
+		if (!options.customMerge) {
+			return deepmerge
+		}
+		var customMerge = options.customMerge(key);
+		return typeof customMerge === 'function' ? customMerge : deepmerge
+	}
+
+	function getEnumerableOwnPropertySymbols(target) {
+		return Object.getOwnPropertySymbols
+			? Object.getOwnPropertySymbols(target).filter(function(symbol) {
+				return target.propertyIsEnumerable(symbol)
+			})
+			: []
+	}
+
+	function getKeys(target) {
+		return Object.keys(target).concat(getEnumerableOwnPropertySymbols(target))
+	}
+
+	function propertyIsOnObject(object, property) {
+		try {
+			return property in object
+		} catch(_) {
+			return false
+		}
+	}
+
+	// Protects from prototype poisoning and unexpected merging up the prototype chain.
+	function propertyIsUnsafe(target, key) {
+		return propertyIsOnObject(target, key) // Properties are safe to merge if they don't exist in the target yet,
+			&& !(Object.hasOwnProperty.call(target, key) // unsafe if they exist up the prototype chain,
+				&& Object.propertyIsEnumerable.call(target, key)) // and also unsafe if they're nonenumerable.
+	}
+
+	function mergeObject(target, source, options) {
+		var destination = {};
+		if (options.isMergeableObject(target)) {
+			getKeys(target).forEach(function(key) {
+				destination[key] = cloneUnlessOtherwiseSpecified(target[key], options);
+			});
+		}
+		getKeys(source).forEach(function(key) {
+			if (propertyIsUnsafe(target, key)) {
+				return
+			}
+
+			if (propertyIsOnObject(target, key)) {
+				if (options.isEmpty && options.isEmpty(source[key])) {
+					destination[key] = cloneUnlessOtherwiseSpecified(target[key], options);
+				} else if (options.isMergeableObject(source[key])) {
+					destination[key] = getMergeFunction(key, options)(target[key], source[key], options);
+				} else {
+					destination[key] = cloneUnlessOtherwiseSpecified(source[key], options);
+				}
+			} else {
+				destination[key] = cloneUnlessOtherwiseSpecified(source[key], options);
+			}
+		});
+		return destination
+	}
+
+	function deepmerge(target, source, options) {
+		options = options || {};
+		options.arrayMerge = options.arrayMerge || defaultArrayMerge;
+		options.isMergeableObject = options.isMergeableObject || isMergeableObject;
+		// cloneUnlessOtherwiseSpecified is added to `options` so that custom arrayMerge()
+		// implementations can use it. The caller may not replace it.
+		options.cloneUnlessOtherwiseSpecified = cloneUnlessOtherwiseSpecified;
+
+		var sourceIsArray = Array.isArray(source);
+		var targetIsArray = Array.isArray(target);
+		var sourceAndTargetTypesMatch = sourceIsArray === targetIsArray;
+
+		if (!sourceAndTargetTypesMatch) {
+			return cloneUnlessOtherwiseSpecified(source, options)
+		} else if (sourceIsArray) {
+			return options.arrayMerge(target, source, options)
+		} else {
+			return mergeObject(target, source, options)
+		}
+	}
+
+	deepmerge.all = function deepmergeAll(array, options) {
+		if (!Array.isArray(array)) {
+			throw new Error('first argument should be an array')
+		}
+
+		return array.reduce(function(prev, next) {
+			return deepmerge(prev, next, options)
+		}, {})
+	};
+
+	var deepmerge_1 = deepmerge;
+
+	return deepmerge_1;
+
+})));

index.js

@@ -63,8 +63,14 @@ function mergeObject(target, source, options) {
 			return
 		}
 
-		if (propertyIsOnObject(target, key) && options.isMergeableObject(source[key])) {
-			destination[key] = getMergeFunction(key, options)(target[key], source[key], options)
+		if (propertyIsOnObject(target, key)) {
+			if (options.isEmpty && options.isEmpty(source[key])) {
+				destination[key] = cloneUnlessOtherwiseSpecified(target[key], options)
+			} else if (options.isMergeableObject(source[key])) {
+				destination[key] = getMergeFunction(key, options)(target[key], source[key], options)
+			} else {
+				destination[key] = cloneUnlessOtherwiseSpecified(source[key], options)
+			}
 		} else {
 			destination[key] = cloneUnlessOtherwiseSpecified(source[key], options)
 		}