More lenses 🕶

CHANGELOG.md

@@ -1,3 +1,7 @@
+# 1.68.0
+- Add `objectLens`
+- Add `arrayLens`
+
 # 1.67.0
 - Improvements to `unwind`: use `_.castArray` to avoid unwinding strings and other array-likes
 - Add `unwindArray`

README.md

@@ -645,6 +645,10 @@ Returns a function that will set a lens to `false`
 `value -> arrayLens -> includeLens`
 An include lens represents membership of a value in a set. It takes a value and lens and returns a new lens - kind of like a "writeable computed" from MobX or Knockout. The view and set functions allow you to read and write a boolean value for whether or not a value is in an array. If you change to true or false, it will set the underlying array lens with a new array either without the value or with it pushed at the end.
 
+#### optionLens
+`value -> arrayLens -> optionLens`
+Like `includeLens`, `optionLens` takes a value and lens and returns a new lens. The view and set functions allow you to read and write a boolean value for whether the value passed to the `optionLens` is currently selected (meaning whether it matches the value stored in the underlying lens). Setting the `optionLens` to true "selects" its value (sets the value of the underlying lens to it); setting it to false sets the underlying value to `null`.
+
 #### domLens.value
 `lens -> {value, onChange}` Takes a lens and returns a value/onChange pair that views/sets the lens appropriately. `onChange` sets with `e.target.value` (or `e` if that path isn't present).
 Example:
@@ -676,6 +680,9 @@ Takes a value and returns a function lens for that value. Mostly used for testin
 ### objectLens
 Takes a value and returns a object lens for that value. Mostly used for testing and mocking purposes.
 
+### arrayLens
+Takes a value and returns an array lens for that value. Mostly used for testing and mocking purposes.
+
 ### stateLens
 `([value, setValue]) -> lens` Given the popularity of React, we decided to include this little helper that converts a `useState` hook call to a lens. Ex: `let lens = stateLens(useState(false))`. You generally won't use this directly since you can pass the `[value, setter]` pair directly to lens functions
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "futil-js",
-  "version": "1.67.0",
+  "version": "1.68.0",
   "description": "F(unctional) util(ities). Resistance is futile.",
   "main": "lib/futil-js.js",
   "scripts": {

src/lens.js

@@ -14,6 +14,13 @@ export let objectLens = val => ({
     val = x
   },
 })
+export let arrayLens = val => {
+  let result = [val]
+  result.push(x => {
+    result[0] = x
+  })
+  return result
+}
 
 // Lens Conversion
 export let fnToObj = fn => ({
@@ -52,6 +59,11 @@ export let includeLens = (value, ...lens) => ({
   set: x => set(_.uniq(toggleElementBy(!x, value, view(...lens))), ...lens),
 })
 
+export let optionLens = (value, ...lens) => ({
+  get: () => _.equals(value, view(...lens)),
+  set: x => set(x ? value : null, ...lens),
+})
+
 // Lens Manipulation
 //let construct = (...lens) => (lens[1] ? lensProp(...lens) : lens[0])
 let lensPair = (get, set) => ({ get, set })

test/lens.spec.js

@@ -19,6 +19,12 @@ describe('Lens Functions', () => {
       l.set(5)
       expect(l.get()).to.equal(5)
     })
+    it('arrayLens', () => {
+      let l = F.arrayLens(1)
+      expect(l[0]).to.equal(1)
+      l[1](5)
+      expect(l[0]).to.equal(5)
+    })
   })
   describe('Conversion', () => {
     it('fnToObj', () => {
@@ -78,6 +84,21 @@ describe('Lens Functions', () => {
       expect(F.view(includesB)).to.be.true
       expect(object.arr).to.deep.equal(['a', 'c', 'd', 'b'])
     })
+    it('optionLens', () => {
+      let object = { selected: 'a' }
+      let optionA = F.optionLens('a', 'selected', object)
+      let optionB = F.optionLens('b', 'selected', object)
+      expect(F.view(optionA)).to.be.true
+      expect(F.view(optionB)).to.be.false
+      F.on(optionB)()
+      expect(F.view(optionA)).to.be.false
+      expect(F.view(optionB)).to.be.true
+      expect(object.selected).to.equal('b')
+      F.off(optionB)()
+      expect(F.view(optionA)).to.be.false
+      expect(F.view(optionB)).to.be.false
+      expect(object.selected).to.deep.equal(null)
+    })
   })
   describe('Manipulation', () => {
     it('view', () => {
@@ -196,14 +217,7 @@ describe('Lens Functions', () => {
   })
   describe('additional implicit lens formats', () => {
     it('arrayLens', () => {
-      let arrayLens = val => {
-        let result = [val]
-        result.push(x => {
-          result[0] = x
-        })
-        return result
-      }
-      let lens = arrayLens(false)
+      let lens = F.arrayLens(false)
       F.on(lens)()
       expect(lens[0]).to.be.true
       F.off(lens)()