time-to-botec/squiggle/node_modules/@stdlib/utils/merge/README.md

470 lines
8.1 KiB
Markdown
Raw Normal View History

<!--
@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.
-->
# Merge
> Merge and extend objects.
<section class="usage">
## Usage
```javascript
var merge = require( '@stdlib/utils/merge' );
```
#### merge( target, source1\[, source2\[,...,sourceN]] )
Merges and extends a target `object`.
```javascript
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`.
```javascript
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`.
```javascript
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][@stdlib/utils/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.
```javascript
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.
```javascript
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][@stdlib/utils/copy].
```javascript
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`.
```javascript
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`.
```javascript
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`.
```javascript
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`.
```javascript
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'
}
*/
```
</section>
<!-- /.usage -->
<section class="notes">
* * *
## Notes
- The target `object` is **mutated**.
```javascript
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.
```javascript
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][@stdlib/utils/copy] or assigned:
- `Boolean`
- `String`
- `Number`
- `Date`
- `RegExp`
- `Array`
- `Int8Array`
- `Uint8Array`
- `Uint8ClampedArray`
- `Init16Array`
- `Uint16Array`
- `Int32Array`
- `Uint32Array`
- `Float32Array`
- `Float64Array`
- `Buffer` ([Node.js][node-buffer])
- `Set`
- `Map`
- `Error`
- `URIError`
- `ReferenceError`
- `SyntaxError`
- `RangeError`
- Support for deep merging class instances is inherently [**fragile**][@stdlib/utils/copy].
- `Number`, `String`, or `Boolean` objects are merged as [primitives][@stdlib/utils/copy].
- Functions are **not** [deep copied][@stdlib/utils/copy].
</section>
<!-- /.notes -->
<section class="examples">
* * *
## Examples
<!-- eslint no-undef: "error" -->
```javascript
var merge = require( '@stdlib/utils/merge' );
var target;
var source;
var out;
target = {
'a': 'beep',
'b': 'boop',
'c': {
'c1': 'woot',
'c2': false,
'c3': {
'c3a': [ 1, 2 ],
'c3b': null
}
},
'd': [ 1, 2, 3 ]
};
source = {
'b': 3.141592653589793,
'c': {
'c1': 'bap',
'c3': {
'c3b': 5,
'c3c': 'bop'
},
'c4': 1337,
'c5': new Date()
},
'd': [ 4, 5, 6 ],
'e': true
};
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
}
*/
```
</section>
<!-- /.examples -->
<section class="links">
[@stdlib/utils/copy]: https://www.npmjs.com/package/@stdlib/utils/tree/main/copy
[node-buffer]: http://nodejs.org/api/buffer.html
</section>
<!-- /.links -->