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Merge and extend objects.
import merge from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-merge@deno/mod.js';You can also import the following named exports from the package:
import { factory } from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-merge@deno/mod.js';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'
}
*/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:
booleanindicating whether to deep copy merged values. Deep copying prevents shared references and sourceobjectmutation. Default:true. - override: defines the merge strategy. If
true, sourceobjectvalues will always override targetobjectvalues. Iffalse, source values never override target values (useful for adding, but not overwriting, properties). To define a custom merge strategy, provide afunction. Default:true. - extend:
booleanindicating whether new properties can be added to the targetobject. Iffalse, 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 );
// => falseTo 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 trueTo 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'
}
*/-
The target
objectis 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 emptyobjectas the first argument.var target = { 'a': 'beep' }; var source = { 'b': 'boop' }; var out = merge( {}, target, source ); console.log( out === target ); // => false
-
Only plain JavaScript
objectsare merged and extended. The following values/types are either deep copied or assigned:BooleanStringNumberDateRegExpArrayInt8ArrayUint8ArrayUint8ClampedArrayInit16ArrayUint16ArrayInt32ArrayUint32ArrayFloat32ArrayFloat64ArrayBuffer(Node.js)SetMapErrorURIErrorReferenceErrorSyntaxErrorRangeError
-
Support for deep merging class instances is inherently fragile.
-
Number,String, orBooleanobjects are merged as primitives. -
Functions are not deep copied.
import merge from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-merge@deno/mod.js';
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
}
*/@stdlib/utils-copy: copy or deep clone a value to an arbitrary depth.
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.
See LICENSE.
Copyright © 2016-2025. The Stdlib Authors.
