Easily compare changes in JSON-like values. This can be especially useful when you want to compare an incoming payload with a counterpart stored in a database.
npm i json-changesFirst, let's define our flags in a file we'll call permissions.js:
const diff = require('json-changes')
const before = { hello: 'world', foo: 'bar', thisPropertyNoLongerExists: true }
const after = { hello: 'world', foo: 'not bar' }
const comparison = diff(before, after)
// returns:
{
before: {
foo: 'bar',
thisPropertyNoLongerExists: true
},
after: {
// Only properties that changed are included
foo: 'not bar',
// Properties that have been removed have an undefined value;
thisPropertyNoLongerExists: undefined
}
}It works recursively in nested objects as well:
const before = { nestedObj: {} }
const after = { nestedObj: { evenMoreNestedObject: { thisPropIsNew: 'Hello, new property!' } } }
const comparison = diff(before, after)
// returns:
{
before: {
nestedObj: { evenMoreNestedObject: undefined }
},
after: {
nestedObj: {
evenMoreNestedObject: {
thisPropIsNew: 'Hello, new property!'
}
}
}
}Encountering an undefined value in the comparison means that the property either did not exist in before or was removed in after.
json-changes is primarily meant to be used to compare JSON, so undefined is assumed to never be used in the payloads being compared.