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* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var objectKeys = require( '@stdlib/utils/keys' );
var isObject = require( '@stdlib/assert/is-object' );
var hasOwnProp = require( '@stdlib/assert/has-own-property' );
var isBuffer = require( '@stdlib/assert/is-buffer' );
var isFunction = require( '@stdlib/assert/is-function' );
var typeOf = require( '@stdlib/utils/type-of' );
var deepCopy = require( '@stdlib/utils/copy' );
// MAIN //
/**
* Merges a source object into a target object.
*
* @private
* @param {Object} target - target object
* @param {Object} source - source object
* @param {number} level - merge level
* @param {boolean} copy - indicates whether to perform a deep copy of merged values
* @param {(boolean|Function)} override - defines the merge strategy
* @param {boolean} extend - indicates whether new properties can be added to the target object
*/
function deepMerge( target, source, level, copy, override, extend ) {
var hasProp;
var isFunc;
var name;
var keys;
var curr;
var key;
var val;
var tmp;
var i;
// Determine if we were provided a custom override strategy:
isFunc = isFunction( override );
// Decrement the level:
level -= 1;
// Loop through the source keys and implement the merge strategy...
keys = objectKeys( source );
for ( i = 0; i < keys.length; i++ ) {
key = keys[ i ];
hasProp = hasOwnProp( target, key );
// Can we add new properties to the target?
if ( !hasProp && !extend ) {
continue;
}
val = source[ key ];
if ( hasProp ) {
curr = target[ key ];
name = typeOf( curr );
// Should we recurse to perform a deep(er) merge? (only if both the current value and the proposed value are objects and the level is > 0)
if (
!isBuffer( curr ) &&
name === 'object' &&
isObject( val ) &&
level
) {
deepMerge( curr, val, level, copy, override, extend );
continue;
}
// Should we apply a custom merge (override) strategy?
if ( isFunc ) {
tmp = override( curr, val, key );
// WARNING: the following check does NOT prevent shared (leaky) nested references. We only check for top-level reference equality. We will assume that the user knows best, given their having provided a custom override strategy.
if ( copy && tmp !== curr && tmp === val ) {
tmp = deepCopy( tmp );
}
target[ key ] = tmp;
}
// Are we allowed to override an existing target value?
else if ( override ) {
if ( copy ) {
target[ key ] = deepCopy( val );
} else {
target[ key ] = val;
}
}
}
// New property to be added to target object. Should we deep copy the source value?
else if ( copy ) {
target[ key ] = deepCopy( val );
}
// Perform a simple assignment...
else {
target[ key ] = val;
}
}
}
// EXPORTS //
module.exports = deepMerge;
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