Patch JSON

Patch JSON is utility and YAML-based language to make changes over JSON and produce new updated JSON.

Contents

• Introduction
• Getting started
• Usage
• Actions
  • Common actions
    • SET
    • UNSET
  • Array actions
    • PUSH
    • UNSHIFT
    • INSERT
    • DELETE
• API
  • Methods
  • Errors
• References

Introduction

You can use few approaches to reach element from JSON object.

    {
        "component": {
            "menu": {
                "title": "File Menu",
                "items": [
                    {"id": "open", "title": "open"},
                    {"id": "close", "title": "close"}
                ]
            }
        }
    }

1. Dot notation. This approach is recommended only for simple cases, that don't require any expressions. For instance:

   • Getting menu title: component.menu.title
   • Getting "open" item of menu: component.menu.items[0]

2. JSONPath notation. More powerfull notation that allows us to use expressions to get element:

   • Getting menu title: $.component.menu.title
   • Getting "open" item of menu: $.component.menu.items[?(@.id === 'open')]

Common patch structure:

    component.menu.title:
        - ACTION: <ACTION NAME>
        [ VALUE: <VALUE> ]
        - ACTION: <ACTION NAME>
    component.menu:
        - ACTION: <ACTION NAME>
        [ VALUE: <VALUE> ]
        - ACTION: <ACTION NAME>

This structure defines sequence of actions that should applied to json.

Getting started

Instal json-patch into the project:

npm install patch-json --save

or

yarn add patch-json

Usage

Let's take a look at example of patch-json usage:

const fs = require('fs');
const jsonPatch = require('patch-json');
 
let jsonContent = fs.readFileSync('content.json');
let patch = fs.readFileSync('patch.yaml');
// Apply patch to loaded json data:
let newJson = jsonPatch.patch(jsonContent, patch);

Common actions

SET

Add new or modify exists node of the JSON object.

Parameters

• ACTION: SET
• VALUE - {any} New value

component.menu:
  - ACTION: SET
    VALUE:
      newProperty:
        prop1: value1

UNSET

Remove node from JSON object

Parameters

• ACTION: UNSET

component.menu.title:
  - ACTION: REMOVE

Array actions

These actions can be applied only to the arrays.

PUSH

Append new item to the end of an array

Parameters

• ACTION: PUSH
• VALUE - {any} New value

component:
    - ACTION: PUSH
      VALUE:
        newProperty:
            prop1: value1

UNSHIFT

Add item to the beginning of an array

Parameters

• ACTION: UNSHIFT
• VALUE - {any} New value

component:
  - ACTION: UNSHIFT
    VALUE:
      newProperty:
        prop1: value1

INSERT

Insert item into array

Parameters

• ACTION: INSERT
• [AFTER] or [BEFORE] : {String} JSONPath value
• VALUE: {any} inserted value

components:
  - ACTION: INSERT
    AFTER: "[?(@.id === 'search')]"
    VALUE:
      id: 'delete'
  - ACTION: INSERT
    BEFORE: "[?(@.id === 'results')]"
    VALUE:
      id: 'users'

DELETE

Delete item from array

Parameters

• ACTION: DELETE
• ITEM: {String} JSONPath value

components:
  - ACTION: DELETE
    ITEM: "[?(@.id === 'search')]"

API

Methods

patch(jsonString, yamlString) -> Object

validate(yamlString) -> Boolean

Errors

Patch JSON uses exceptions to process errors. Error object contains name property that defines error type:

1. JSON_VALIDATION_ERROR
2. YAML_VALIDATION_ERROR
3. YAML_STRUCTURE_ERROR
4. PATCH_ERROR

Also it contains message and stack properties to get additional info about error.

    try {
        jsonPath.patch(jsonString, yamlString)
    } catch(ex) {
        if (ex.name === 'JSON_VALIDATION_ERROR') {
            
        } else if (ex.name === 'YAML_VALIDATION_ERROR') {
        
        } else if (ex.name === 'YAML_STRUCTURE_ERROR') {
        
        } else if (ex.name === 'PATCH_ERROR') {
            
        }
    
    }

References

1. JSONPath syntax description