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About stdlib...

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

Merge

NPM version Build Status Coverage Status

Merge and extend objects.

Usage

import merge from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-merge@esm/index.mjs';

You can also import the following named exports from the package:

import { factory } from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-merge@esm/index.mjs';

merge( target, source1[, source2[,...,sourceN]] )

Merges and extends a target object.

var target = {
    'a': 'beep'
};
var source = {
    'a': 'boop',
    'b': 'bap'
};

var out = merge( target, source );
/* returns
    {
        'a': 'boop',
        'b': 'bap'
    }
*/

The function supports merging multiple source objects.

var target = {
    'a': 'beep'
};
var source1 = {
    'b': 'boop'
};
var source2 = {
    'c': 'cat'
};

var out = merge( target, source1, source2 );
/* returns
    {
        'a': 'beep',
        'b': 'boop',
        'c': 'cat'
    }
*/

merge.factory( options )

Returns a custom merge function for merging and extending objects.

var opts = {
    'level': 100,
    'copy': true,
    'override': true,
    'extend': true
};

var m = merge.factory( opts );

The function accepts the following options:

  • level: limits the merge depth. The default merge strategy is a deep (recursive) merge. Default: +infinity.
  • copy: boolean indicating whether to deep copy merged values. Deep copying prevents shared references and source object mutation. Default: true.
  • override: defines the merge strategy. If true, source object values will always override target object values. If false, source values never override target values (useful for adding, but not overwriting, properties). To define a custom merge strategy, provide a function. Default: true.
  • extend: boolean indicating whether new properties can be added to the target object. If false, only shared properties are merged. Default: true.

The default merge is a deep (recursive) merge.

var m = merge.factory( {} );

var target = {
    'a': {
        'b': {
            'c': 5
        },
        'd': 'beep'
    }
};
var source = {
    'a': {
        'b': {
            'c': 10
        }
    }
};

var out = m( target, source );
/* returns
    {
        'a': {
            'b': {
                'c': 10
            },
            'd': 'beep'
        }
    }
*/

To limit the merge depth, set the level option.

var m = merge.factory({
    'level': 2
});

var target = {
    '1': {
        'a': 'beep',
        '2': {
            '3': null,
            'b': [ 5, 6, 7 ]
        }
    }
};

var source = {
    '1': {
        'b': 'boop',
        '2': {
            '3': [ 1, 2, 3 ]
        }
    }
};

var out = m( target, source );
/* returns
    {
        '1': {
            'a': 'beep',
            'b': 'boop',
            '2': {
                '3': [ 1, 2, 3 ]
            }
        }
    }
*/

By default, merged values are deep copied.

var m = merge.factory( {} );

var target = {
    'a': null
};
var source = {
    'a': {
        'b': [ 1, 2, 3 ]
    }
};

var out = m( target, source );

console.log( out.a.b === source.a.b );
// => false

To allow shared references, set the copy option to false.

var m = merge.factory({
    'copy': false
});

var target = {};

var source = {
    'a': [ 1, 2, 3 ]
};

var out = m( target, source );

var bool = ( out.a === source.a );
// returns true

To prevent existing properties from being overridden, set the override option to false.

var m = merge.factory({
    'override': false
});

var target = {
    'a': 'beep',
    'b': 'boop'
};

var source = {
    'a': null,
    'c': 'bop'
};

var out = m( target, source );
/* returns
    {
        'a': 'beep',
        'b': 'boop',
        'c': 'bop'
    }
*/

Alternatively, to define a custom merge strategy, set the override option to a function.

function strategy( a, b, key ) {
    /* Parameters:
        a => target value
        b => source value
        key => object key
    */
    if ( key === 'a' ) {
        return b;
    }
    if ( key === 'b' ) {
        return a;
    }
    return 'bebop';
}

var m = merge.factory({
    'override': strategy
});

var target = {
    'a': 'beep',
    'b': 'boop',
    'c': 1234
};

var source = {
    'a': null,
    'b': {},
    'c': 'bop'
};

var out = m( target, source );
/* returns
    {
        'a': null,
        'b': 'boop',
        'c': 'bebop'
    }
*/

To prevent non-existent properties from being added to the target object, set the extend option to false.

var m = merge.factory({
    'extend': false
});

var target = {
    'a': 'beep',
    'b': 'boop'
};

var source = {
    'b': 'hello',
    'c': 'world'
};

var out = m( target, source );
/* returns
    {
        'a': 'beep',
        'b': 'hello'
    }
*/

Notes

  • The target object is mutated.

    var target = {
    'a': 'beep'
};
var source = {
    'b': 'boop'
};

var out = merge( target, source );

console.log( out === target );
// => true

console.log( target.b );
// => 'boop'

    To return a new object, provide an empty object as the first argument.

    var target = {
    'a': 'beep'
};
var source = {
    'b': 'boop'
};

var out = merge( {}, target, source );

console.log( out === target );
// => false

  • Only plain JavaScript objects are merged and extended. The following values/types are either deep copied or assigned:

    • Boolean
    • String
    • Number
    • Date
    • RegExp
    • Array
    • Int8Array
    • Uint8Array
    • Uint8ClampedArray
    • Init16Array
    • Uint16Array
    • Int32Array
    • Uint32Array
    • Float32Array
    • Float64Array
    • Buffer (Node.js)
    • Set
    • Map
    • Error
    • URIError
    • ReferenceError
    • SyntaxError
    • RangeError

  • Support for deep merging class instances is inherently fragile.

  • Number, String, or Boolean objects are merged as primitives.

  • Functions are not deep copied.

Examples

<!DOCTYPE html>
<html lang="en">
<body>
<script type="module">

import merge from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-merge@esm/index.mjs';

var target = {
    'a': 'beep',
    'b': 'boop',
    'c': {
        'c1': 'woot',
        'c2': false,
        'c3': {
            'c3a': [ 1, 2 ],
            'c3b': null
        }
    },
    'd': [ 1, 2, 3 ]
};

var source = {
    'b': 3.141592653589793,
    'c': {
        'c1': 'bap',
        'c3': {
            'c3b': 5,
            'c3c': 'bop'
        },
        'c4': 1337,
        'c5': new Date()
    },
    'd': [ 4, 5, 6 ],
    'e': true
};

var out = merge( {}, target, source );
/* returns
    {
        'a': 'beep',
        'b': 3.141592653589793,
        'c': {
            'c1': 'bap',
            'c2': false,
            'c3': {
                'c3a': [ 1, 2 ],
                'c3b': 5,
                'c3c': 'bop'
            },
            'c4': 1337,
            'c5': <Date>
        },
        'd': [ 4, 5, 6 ],
        'e': true
    }
*/

</script>
</body>
</html>

See Also

Notice

This package is part of stdlib, a standard library with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

Chat

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.