fix: serialization of Units without a value, see #1240

HISTORY.md

@@ -1,5 +1,10 @@
 # History
 
+# unpublished changes since 12.4.2
+
+- Fix: serialization of Units without a value, see #1240.
+
+
 # 2024-04-24, 12.4.2
 
 - Fix #3192: function `isNaN` returns `false` for `NaN` units in a matrix or

src/type/unit/Unit.js

@@ -902,7 +902,7 @@ export const createUnitClass = /* #__PURE__ */ factory(name, dependencies, ({
     return {
       mathjs: 'Unit',
       value: this._denormalize(this.value),
-      unit: this.formatUnits(),
+      unit: this.units.length > 0 ? this.formatUnits() : null,
       fixPrefix: this.fixPrefix
     }
   }
@@ -915,7 +915,7 @@ export const createUnitClass = /* #__PURE__ */ factory(name, dependencies, ({
    * @return {Unit}
    */
   Unit.fromJSON = function (json) {
-    const unit = new Unit(json.value, json.unit)
+    const unit = new Unit(json.value, json.unit ?? undefined)
     unit.fixPrefix = json.fixPrefix || false
     return unit
   }

test/unit-tests/json/replacer.test.js

@@ -72,6 +72,20 @@ describe('replacer', function () {
     assert.deepStrictEqual(JSON.stringify(u, replacer), json)
   })
 
+  it('should stringify a Unit with a value only', function () {
+    const u = new math.Unit(5)
+    const json = '{"mathjs":"Unit","value":5,"unit":null,"fixPrefix":false}'
+    assert.deepStrictEqual(JSON.stringify(u), json)
+    assert.deepStrictEqual(JSON.stringify(u, replacer), json)
+  })
+
+  it('should stringify a Unit without a value', function () {
+    const u = new math.Unit(null, 'cm')
+    const json = '{"mathjs":"Unit","value":null,"unit":"cm","fixPrefix":false}'
+    assert.deepStrictEqual(JSON.stringify(u), json)
+    assert.deepStrictEqual(JSON.stringify(u, replacer), json)
+  })
+
   it('should stringify a Matrix, dense', function () {
     const m = math.matrix([[1, 2], [3, 4]], 'dense')
     const json = '{"mathjs":"DenseMatrix","data":[[1,2],[3,4]],"size":[2,2]}'

test/unit-tests/json/reviver.test.js

@@ -70,6 +70,26 @@ describe('reviver', function () {
     assert.deepStrictEqual(obj, u)
   })
 
+  it('should parse a stringified Unit with a value only', function () {
+    const json = '{"mathjs":"Unit","value":5,"unit":null,"fixPrefix":false}'
+    const u = new math.Unit(5)
+
+    const obj = JSON.parse(json, reviver)
+
+    assert(obj instanceof math.Unit)
+    assert.deepStrictEqual(obj, u)
+  })
+
+  it('should parse a stringified Unit without a value', function () {
+    const json = '{"mathjs":"Unit","value":null,"unit":"cm","fixPrefix":false}'
+    const u = new math.Unit(null, 'cm')
+
+    const obj = JSON.parse(json, reviver)
+
+    assert(obj instanceof math.Unit)
+    assert.deepStrictEqual(obj, u)
+  })
+
   it('should parse a stringified Range (2)', function () {
     const json = '{"mathjs":"Range","start":2,"end":10,"step":2}'
     const r = new math.Range(2, 10, 2)