fix: function get now returns null instead of undefined when a property doesn't exist

josdejong · josdejong · commit 95d1764700c4 · 2024-11-08T16:43:07.000+01:00
BREAKING CHANGE:
Function `get` now returns `null` instead of `undefined` when a property doesn't exist
diff --git a/reference/functions.md b/reference/functions.md
@@ -797,7 +797,7 @@ jsonquery(data, 'filter(not(.age == 18))')
 
 ## exists
 
-Returns true if the value at the provided path exists, and returns false when it is `undefined`.
+Returns `true` if the property at the provided path exists. Returns `true` too when the properties value contains a value `null`, `false` or `0`.
 
 ```text
 exists(path)
@@ -807,18 +807,22 @@ Examples:
 
 ```js
 const data = [
-  { "name": "Chris", "details": { "age": 16 } },
-  { "name": "Emily" },
-  { "name": "Joe", "details": { "age": 18 } }
+  { "name": "Joe", "details": { "age": 16 } },
+  { "name": "Oliver" },
+  { "name": "Sarah", "details": { "age": 18 } },
+  { "name": "Dave", "details": null },
 ]
 
 jsonquery(data, 'filter(exists(.details))')
 // [
-//   { "name": "Chris", "details": { "age": 16 } },
-//   { "name": "Joe", "details": { "age": 18 } }
+//   { "name": "Joe", "details": { "age": 16 } },
+//   { "name": "Sarah", "details": { "age": 18 } },
+//   { "name": "Dave", "details": null }
 // ]
 
+jsonquery({ }, ["exists", "value"]) // false
 jsonquery({ "value": null }, ["exists", "value"]) // true
+jsonquery({ "value": undefined }, ["exists", "value"]) // false
 ```
 
 ## in
diff --git a/src/compile.test.ts b/src/compile.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, test } from 'vitest'
+import { bench, describe, expect, test } from 'vitest'
 import { compile } from './compile'
 import { buildFunction } from './functions'
 import type { JSONQuery, JSONQueryCompileOptions } from './types'
@@ -53,7 +53,7 @@ describe('compile', () => {
     })
 
     test('should return undefined in case of a non existing path', () => {
-      expect(go({}, ['get', 'foo', 'bar'])).toEqual(undefined)
+      expect(go({}, ['get', 'foo', 'bar'])).toEqual(null)
     })
 
     test('should get a path using function get', () => {
@@ -179,15 +179,15 @@ describe('compile', () => {
         actualErr = err
       }
 
-      expect(actualErr?.message).toBe("Cannot read properties of undefined (reading 'reduce')")
+      expect(actualErr?.message).toBe("Cannot read properties of null (reading 'reduce')")
       expect(actualErr?.jsonquery).toEqual([
         { data: scoreData, query },
         {
           data: scoreData.participants,
           query: ['map', ['pipe', ['get', 'scores'], ['sum']]]
         },
         { data: { name: 'Emily', age: 19 }, query: ['pipe', ['get', 'scores'], ['sum']] },
-        { data: undefined, query: ['sum'] }
+        { data: null, query: ['sum'] }
       ])
     })
   })
@@ -704,7 +704,7 @@ describe('compile', () => {
     expect(go({ a: '' }, ['exists', ['get', 'a']])).toEqual(true)
     expect(go({ nested: { a: 2 } }, ['exists', ['get', 'nested', 'a']])).toEqual(true)
 
-    expect(go({ a: undefined }, ['exists', ['get', 'a']])).toEqual(false)
+    expect(go({ a: undefined }, ['exists', ['get', 'a']])).toEqual(true)
     expect(go({}, ['exists', ['get', 'a']])).toEqual(false)
     expect(go({}, ['exists', ['get', 'nested', 'a']])).toEqual(false)
     expect(go({}, ['exists', ['get', 'sort']])).toEqual(false)
diff --git a/src/functions.ts b/src/functions.ts
@@ -6,6 +6,7 @@ import type {
   Getter,
   JSONPath,
   JSONQuery,
+  JSONQueryFunction,
   JSONQueryObject,
   JSONQueryProperty
 } from './types'
@@ -52,12 +53,12 @@ export const functions: FunctionBuildersMap = {
 
   get: (...path: JSONPath) => {
     if (path.length === 0) {
-      return (data: unknown) => data
+      return (data: unknown) => data ?? null
     }
 
     if (path.length === 1) {
       const prop = path[0]
-      return (data: unknown) => data?.[prop]
+      return (data: unknown) => data?.[prop] ?? null
     }
 
     return (data: unknown) => {
@@ -67,7 +68,7 @@ export const functions: FunctionBuildersMap = {
         value = value?.[prop]
       }
 
-      return value
+      return value ?? null
     }
   },
 
@@ -210,7 +211,16 @@ export const functions: FunctionBuildersMap = {
   and: buildFunction((a, b) => a && b),
   or: buildFunction((a, b) => a || b),
   not: buildFunction((a: unknown) => !a),
-  exists: buildFunction((a: unknown) => a !== undefined),
+  exists: (path: JSONQueryFunction) => {
+    const parentPath = path.slice(1)
+    const key = parentPath.pop()
+    const getter = functions.get(...parentPath)
+
+    return (data: unknown) => {
+      const parent = getter(data)
+      return !!parent && Object.hasOwnProperty.call(parent, key)
+    }
+  },
 
   eq: buildFunction((a, b) => a === b),
   gt: buildFunction((a, b) => a > b),
