This is a fork of @boschni/json-merger, as he hasn't had any GitHub activity since April 2023. I am taking over package maintenance for now, but if he decides he wants to start again, I'll be happy to merge any changes back into his repo.
Merge JSON (or YAML) files and objects with operations like $import $remove $replace $merge and more.
javascript
var jsonMerger = require("json-merger");
var result = jsonMerger.mergeFile("a.json");
a.json:
{
"$merge": {
"source": {
"$import": "b.json"
},
"with": {
"prop1": {
"$replace": {
"prop1a": "this will replace b.json's property prop1"
}
},
"prop2": {
"prop2a": "this will merge with b.json's property prop2"
}
}
}
}
b.json:
{
"prop1": {
"prop1b": "will be replaced"
},
"prop2": {
"prop2b": "will be merged"
}
}
result
{
"prop1": {
"prop1a": "this will replace b.json's property prop1"
},
"prop2": {
"prop2a": "this will merge with b.json's property prop2",
"prop2b": "will be merged"
}
}
javascript
var jsonMerger = require("json-merger");
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json:
{
"a": "some value"
}
b.json:
{
"b": "some other value"
}
result
{
"a": "some value",
"b": "some other value"
}
javascript
var jsonMerger = require("json-merger");
var object = {
a: {
aa: "some value",
},
b: {
$import: "b.json",
},
};
var result = jsonMerger.mergeObject(object);
b.json:
{
"bb": "some other value"
}
result
{
"a": {
"aa": "some value"
},
"b": {
"bb": "some other value"
}
}
javascript
var jsonMerger = require("json-merger");
var object1 = {
a: [1, 1, 1, 1],
};
var object2 = {
a: [2, 2],
};
var result = jsonMerger.mergeObjects([object1, object2]);
result
{
"a": [2, 2, 1, 1]
}
The actual Merger
class is also exported. The other exports are just shortcut methods.
Using one Merger
instance has some performance advantages because it will cache previously loaded and processed files.
javascript
var Merger = require("json-merger").Merger;
var merger = new Merger();
// the first call will load and process "a.json"
var result1 = merger.mergeFile("a.json");
// the second call will return the cached result
var result2 = merger.mergeFile("a.json");
// clear the caches
merger.clearCaches();
interface Config {
cwd?: string;
errorOnFileNotFound?: boolean;
errorOnRefNotFound?: boolean;
operationPrefix?: string;
params?: object;
stringify?: boolean | "pretty";
defaultArrayMergeOperation: "combine" | "replace" | "concat";
}
The current working directory when importing files. Defaults to process.cwd().
Set this property to false
to disable throwing errors when an imported file does not exist.
Set this property to false
to disable throwing errors when an JSON pointer or JSON path does not exist.
Use this property to override the prefix to indicate a property is an operation like $import.
The default prefix is $
but it is possible to change this to for example@
to use keywords like@import
.
Object that will be available in $expression
operations as $params
variable.
Set this property to true
to stringify the JSON result. Set the property to "pretty"
if the output should be pretty printed.
Set this property to override default merge operation.
Default value is set to "combine"
. Possible values are:
Use $import
to import other JSON or YAML files.
Files imported with $import
are processed before the result is returned.
{
"$import": "a.json"
}
JSON reference syntax is supported. The following example will import the first array item from the someArray
property in a.json
.
{
"$import": "a.json#/someArray/0"
}
When defined as an array, $import
will process and merge the files in order before returning the result.
{
"$import": ["a.json", "b.yaml", "c.json"]
}
When importing a file it is also possible to provide a different $params
object.
Setting this property will override the Config.params
property.
{
"$import": {
"path": "a.json",
"params": {
"prop": "some value that will be available in a.json as $params.prop"
}
}
}
The object syntax is also supported in an array.
{
"$import": [
{
"path": "a.json",
"params": {
"prop": "value1"
}
},
{
"path": "a.json",
"params": {
"prop": "value2"
}
}
]
}
Use $include
to process a file in the current scope.
Use the $merge
operation to merge objects and arrays.
javascript
var result = jsonMerger.mergeFile("a.json");
a.json
{
"$merge": {
"source": {
"a": {
"aa": "some value"
}
},
"with": {
"a": {
"bb": "some other value"
}
}
}
}
result
{
"a": {
"aa": "some value",
"bb": "some other value"
}
}
The $merge
operation is often used with the $import
operation to merge other files from within the JSON itself.
javascript
var result = jsonMerger.mergeFile("a.json");
a.json
{
"$merge": {
"source": {
"$import": "b.json"
},
"with": {
"a": {
"bb": "some other value"
}
}
}
}
b.json
{
"a": {
"aa": "some value"
}
}
result
{
"a": {
"aa": "some value",
"bb": "some other value"
}
}
Use the $remove
operation to remove properties and array items.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"prop1": {
"prop1a": "some value"
},
"prop2": {
"prop2a": "some other value"
}
}
b.json
{
"prop2": {
"$remove": true
}
}
result
{
"prop1": {
"prop1a": "some value"
}
}
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$remove": true
},
{
"$remove": true
}
]
}
result
{
"someArray": [3]
}
Use the $replace
operation to replace properties and array items.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"prop1": {
"prop1a": "some value"
},
"prop2": {
"prop2a": "some other value"
}
}
b.json
{
"prop2": {
"$replace": {
"prop2b": "replaced value"
}
}
}
result
{
"prop1": {
"prop1a": "some value"
},
"prop2": {
"prop2b": "replaced value"
}
}
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [
{
"a": 1
},
{
"b": 2
}
]
}
b.json
{
"someArray": [
{
"$replace": {
"c": 3
}
}
]
}
result
{
"someArray": [
{
"c": 3
},
{
"b": 2
}
]
}
Use the $concat
operation to concatenate two arrays.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1]
}
b.json
{
"someArray": {
"$concat": [2]
}
}
result
{
"someArray": [1, 2]
}
Use the $combine
operation to combine two arrays.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": {
"$combine": [3, 3]
}
}
result
{
"someArray": [3, 3, 3]
}
Use the $append
operation to append an item to an array.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$append": 4
}
]
}
result
{
"someArray": [1, 2, 3, 4]
}
Use the $prepend
operation to prepend an item to an array.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$prepend": 4
}
]
}
result
{
"someArray": [4, 1, 2, 3]
}
Use the $insert
operation to insert an item to an array.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$insert": {
"index": 1,
"value": 4
}
}
]
}
result
{
"someArray": [1, 4, 2, 3]
}
Set $insert.index
to -
to insert an item at the end of the array.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$insert": {
"index": "-",
"value": 4
}
}
]
}
result
{
"someArray": [1, 2, 3, 4]
}
A negative $insert.index
can be used, indicating an offset from the end of the array.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$insert": {
"index": -1,
"value": 4
}
}
]
}
result
{
"someArray": [1, 2, 4, 3]
}
Use the $match
operation to search for a specific array item and merge with that item.
Use $match.index
to match an array item by index.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$match": {
"index": 1,
"value": 4
}
}
]
}
result
{
"someArray": [1, 4, 3]
}
Use $match.path
to match an array item with a JSON pointer.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$match": {
"path": "/1",
"value": 4
}
}
]
}
result
{
"someArray": [1, 4, 3]
}
Use $match.query
to match an array item with a JSON path query.
The following example will search for an array item containing the value 2
and merge it with the value 4
.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$match": {
"query": "$[?(@ == 2)]",
"value": 4
}
}
]
}
result
{
"someArray": [1, 4, 3]
}
Use the $move
operation to move an array item.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$move": 1
}
]
}
result
{
"someArray": [2, 1, 3]
}
Use the $match
operation in conjunction with the $move
operation to move a specific array item.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$match": {
"index": 0,
"value": {
"$move": 1
}
}
}
]
}
result
{
"someArray": [2, 1, 3]
}
Use -
as $move.index
value to move an array item to the end.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$match": {
"index": 0,
"value": {
"$move": "-"
}
}
}
]
}
result
{
"someArray": [2, 3, 1]
}
Use $move.value
to not only move the item but also merge it with a value.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [
{
"a": 1
},
{
"a": 2
},
{
"a": 3
}
]
}
b.json
{
"someArray": [
{
"$match": {
"query": "$[?(@.a == 3)]",
"value": {
"$move": {
"index": 0,
"value": {
"b": 3
}
}
}
}
}
]
}
result
{
"someArray": [
{
"a": 3,
"b": 3
},
{
"a": 1
},
{
"a": 2
}
]
}
Use the $select
operation to select one or multiple values.
Be careful not to create an endless loop by selecting a parent property.
More information about JSON pointers can be found in the JSON pointer specification.
javascript
var result = jsonMerger.mergeFile("a.json");
a.json
{
"prop": {
"$select": "/otherProp"
},
"otherProp": "Should be the value of prop"
}
result
{
"prop": "Should be the value of prop",
"otherProp": "Should be the value of prop"
}
More information about JSON path queries can be found in the JSON path documentation.
javascript
var result = jsonMerger.mergeFile("a.json");
a.json
{
"prop": {
"$select": {
"query": "$.someArray[*]"
}
},
"someArray": [1, 2, 3]
}
result
{
"prop": 1,
"someArray": [1, 2, 3]
}
javascript
var result = jsonMerger.mergeFile("a.json");
a.json
{
"prop": {
"$select": {
"query": "$.someArray[?(@ < 3)]",
"multiple": true
}
},
"someArray": [1, 2, 3]
}
result
{
"prop": [1, 2]
}
javascript
var result = jsonMerger.mergeFile("a.json");
a.json
{
"prop": {
"$select": {
"from": {
"$import": "b.json"
},
"path": "/someArray/2"
}
}
}
b.json
{
"someArray": [1, 2, 3]
}
result
{
"prop": 3
}
Use the $repeat
operation to repeat a value.
operation
{
"$repeat": {
"from": 1,
"to": 4,
"value": "repeat"
}
}
result
["repeat", "repeat", "repeat"]
The current value is available on the scope as $repeat.value
variable.
operation
{
"$repeat": {
"from": 1,
"through": 4,
"value": {
"$expression": "$repeat.value"
}
}
}
result
[1, 2, 3, 4]
operation
{
"$repeat": {
"from": 0,
"through": 10,
"step": 5,
"value": {
"$expression": "$repeat.value"
}
}
}
result
[0, 5, 10]
operation
{
"$repeat": {
"range": "0:-2, 10, 20:30:5",
"value": {
"$expression": "$repeat.value"
}
}
}
result
[0, -1, -2, 10, 20, 25, 30]
operation
{
"$repeat": {
"in": ["a", "b"],
"value": {
"$expression": "$repeat.value"
}
}
}
result
["a", "b"]
The current key is available on the scope as $repeat.key
variable.
operation
{
"$repeat": {
"in": {
"keyA": "valueA",
"keyB": "valueB"
},
"value": {
"$expression": "{key: $repeat.key, value: $repeat.value}"
}
}
}
result
[
{ "key": "keyA", "value": "valueA" },
{ "key": "keyB", "value": "valueB" }
]
The current index is available on the scope as $repeat.index
variable.
operation
{
"$repeat": {
"range": "1:2",
"value": {
"$expression": "$repeat.index"
}
}
}
result
[0, 1]
Use $parent
to get to the parent scope containing the parent $repeat
.
operation
{
"$repeat": {
"range": "0:1",
"value": {
"$repeat": {
"range": "0:1",
"value": {
"$expression": "$parent.$repeat.index + '.' + $repeat.index"
}
}
}
}
}
result
["0.0", "0.1", "1.0", "1.1"]
Use $include
to load other JSON or YAML files and process them in the current scope.
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"someArray": [1, 2, 3]
}
b.json
{
"someArray": [
{
"$include": "remove.json"
}
]
}
remove.json
{
"$remove": true
}
result
{
"someArray": [2, 3]
}
Use the $expression
operation to calculate a value with the help of a JavaScript expression.
The expression has access to the standard built-in JavaScript objects, the current scope and optionally an $input
variable.
javascript
var result = jsonMerger.mergeFile("a.json");
a.json
{
"prop": {
"$expression": "1 + 2"
}
}
result
{
"prop": 3
}
javascript
var result = jsonMerger.mergeFile("b.json");
a.json
{
"add": 2
}
b.json
{
"prop": {
"$expression": {
"expression": "1 + $input",
"input": {
"$import": "a.json#/add"
}
}
}
}
result
{
"prop": 3
}
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
{
"prop": 1
}
b.json
{
"prop": {
"$expression": "$targetProperty + 2"
}
}
result
{
"prop": 3
}
javascript
var result = jsonMerger.mergeFile("a.json", {
params: {
add: 2,
},
});
a.json
{
"prop": {
"$expression": "1 + $params.add"
}
}
result
{
"prop": 3
}
Scopes can be created while processing operation properties.
If for example a $merge.with
is being processed then the merger will create a new scope for the $merge.with
property.
Or if a $repeat.value
property is being processed a new scope is created for the $repeat.value
property.
A scope always has a $source
property but not necessarily a $target
property.
When we are merging object A with object B, then the $target
property in the scope of object A is undefined
because object A is not merged with anything.
It does have a $source
property referring to object A itself.
Object B on the other hand has the processed object A as $target
because object B is being merged with object A.
The $source
property in the scope of object B refers to object B.
If object B had defined a $merge
operation, then the merger would create a new scope for the $merge.source
property and a new scope for the $merge.with
property.
The $target
within the $merge.source
scope would be undefined
because $merge.source
is not merged with anything.
The $target
within the $merge.with
scope is the processed $merge.source
because $merge.with
is being merged with $merge.source
.
The result of the $merge
operation will eventually be merged with object A.
When in the $merge.source
scope it is possible to get to the root (object B) scope using the $root
property or to a parent scope using the $parent
property.
interface Scope {
$params?: any; // $params properties in current scope
$parent?: Scope; // reference to parent scope
$repeat?: ScopeRepeat; // $repeat properties in current scope
$root: Scope; // reference to root scope
$source: any; // reference to the source object
$target?: any; // reference to the target object
}
javascript
var result = jsonMerger.mergeFiles(["a.json", "b.json"]);
a.json
// this is the root scope
{
"prop1": {
"$expression": "$target" // refers to undefined because a.json has no target
},
"prop2": {
"$expression": "$targetProperty" // refers to undefined because a.json has no target
},
"prop3": {
"$expression": "$source" // refers to the unprocessed a.json
},
"prop4": {
"$expression": "$sourceProperty" // refers to the unprocessed a.json#/prop4
},
"prop5": {
"$expression": "$root.$target" // refers to undefined because a.json has no target
},
"prop6": {
"$expression": "$root.$source" // refers to the unprocessed a.json
},
"prop7": {
"$expression": "$parent" // refers to undefined because the current scope has no parent scope
},
}
b.json
// this is the root scope
{
"prop1": {
"$expression": "$target" // refers to the processed a.json
},
"prop2": {
"$expression": "$targetProperty" // refers to the processed a.json#/prop2
},
"prop3": {
"$expression": "$source" // refers to the unprocessed b.json
},
"prop4": {
"$expression": "$sourceProperty" // refers to the unprocessed b.json#/prop4
},
"prop5": {
"$merge": {
"source": { // $merge.source creates a new scope
"prop1": {
"$expression": "$target" // refers to undefined because b.json#/prop5/$merge/source has no target
},
"prop2": {
"$expression": "$targetProperty" // refers to undefined because b.json#/prop5/$merge/source has no target
},
"prop3": {
"$expression": "$source" // refers to the unprocessed b.json#/prop5/$merge/source
},
"prop4": {
"$expression": "$sourceProperty" // refers to the unprocessed b.json#/prop5/$merge/source/prop4
}
"prop5": {
"$expression": "$root.$target" // refers to the processed a.json
}
"prop6": {
"$expression": "$root.$source" // refers to the unprocessed b.json
},
"prop7": {
"$expression": "$parent.$target" // refers to the processed a.json
}
"prop8": {
"$expression": "$parent.$source" // refers to the unprocessed b.json
}
},
"with": { // $merge.with creates a new scope
"prop1": {
"$expression": "$target" // refers to the processed b.json#/prop5/$merge/source
},
"prop2": {
"$expression": "$targetProperty" // refers to the processed b.json#/prop5/$merge/source/prop2
},
"prop3": {
"$expression": "$source" // refers to the unprocessed b.json#/prop5/$merge/with
},
"prop4": {
"$expression": "$sourceProperty" // refers to the unprocessed b.json#/prop5/$merge/with/prop4
},
"prop5": {
"$expression": "$root.$target" // refers to the processed a.json
},
"prop6": {
"$expression": "$root.source" // refers to the unprocessed b.json
},
"prop7": {
"$expression": "$parent.$target" // refers to the processed a.json
},
"prop8": {
"$expression": "$parent.source" // refers to the unprocessed b.json
}
}
}
},
"prop6": {
"$repeat": {
"range": "0:1",
"value": { // $repeat.value creates a new scope with a $repeat property on it
"$repeat": {
"range": "0:1",
"value": { // $repeat.value creates a new scope with a $repeat property on it
"$expression": "'This is item ' + $parent.$repeat.index + '.' + $repeat.index"
}
}
}
}
}
}
You can use json-merger
as a command line tool:
Usage: json-merger [options] <file ...>
Options:
-V, --version output the version number
-p, --pretty pretty-print the output json
-o, --output [file] the output file. Defaults to stdout
-op, --operation-prefix [prefix] the operation prefix. Defaults to $
-am, --default-array-merge-operation [operation] the default array merge operation. Defaults to combine
--error-on-file-not-found throw an error if a file is not found. Defaults to true
--error-on-ref-not-found throw an error if a JSON pointer or JSON path is not found. Defaults to true
-h, --help output usage information
Usage:
json-merger a.json > result.json
json-merger --output result.json a.json
json-merger --output result.json --pretty a.json
Install json-merger
globally to be able to use the command line interface.
npm install -g json-merger
- Add configurable file resolvers to import files from different sources.
- Add configurable (de)serializers to import and export different file formats.