Add u.ifElse

Fixes #12

CHANGELOG.md

@@ -1,7 +1,7 @@
 # Change Log
 
 ## [unreleased]
-* Add `u.if` to conditionally update objects.
+* Add `u.if` and `u.ifElse` to conditionally update objects.
 * Add `u.map` to update all values in an array or object.
 * Replace object outright if null or constant provided as `updates`.
 * Freeze objects returned by helper methods that use `update` like `withDefault`, `map`, `in`, etc. Previously, only `u` did freezing.

README.md

@@ -140,7 +140,7 @@ u({
 
 ### `u.if(predicate(, updates)(, object))`
 
-Apply updates only if `predicate` is truthy or, if `predicate` is a function,
+Apply `updates` only if `predicate` is truthy or, if `predicate` is a function,
 it evaluates to truthy when called with `object`.
 
 ```js
@@ -154,6 +154,23 @@ u({
 // => { a: 3 }
 ```
 
+### `u.ifElse(predicate(, trueUpdates)(, falseUpdates)(, object))`
+
+Apply `trueUpdates` if `predicate` is truthy or, if `predicate` is a function,
+it evaluates to truthy when called with `object`. Otherwise, apply `falseUpdates`.
+
+```js
+var object = { a: 3 };
+function isEven(x) { return x % 2 === 0; }
+function inc(x) { return x + 1; }
+function dec(x) { return x - 1; }
+
+u({
+  a: u.if(isEven, inc),
+}, object);
+// => { a: 2 }
+```
+
 ### `u.map(iteratee(, object))`
 
 If iteratee is a function, map it over the values in `object`.

lib/ifElse.js

@@ -1,16 +1,14 @@
 import update from './update';
 import wrap from './wrap';
 
-function updateIf(predicate, updates, object) {
+function updateIfElse(predicate, trueUpdates, falseUpdates, object) {
   const test = typeof predicate === 'function' ?
     predicate(object) :
     predicate;
 
-  if (!test) {
-    return object;
-  }
+  const updates = test ? trueUpdates : falseUpdates;
 
   return update(updates, object);
 }
 
-export default wrap(updateIf);
+export default wrap(updateIfElse);

lib/index.js

@@ -1,15 +1,18 @@
 import freeze from './freeze';
 import _in from './in';
-import _if from './if';
+import ifElse from './ifElse';
 import map from './map';
 import omit from './omit';
 import reject from './reject';
 import withDefault from './withDefault';
 import update from './update';
 
+import { placeholder as _ } from 'lodash/function/curry';
+
 const u = update;
 
-u.if = _if;
+u.if = ifElse(_, _, {});
+u.ifElse = ifElse;
 u.in = _in;
 u.freeze = freeze;
 u.map = map;

test/ifElse-spec.js

@@ -0,0 +1,42 @@
+import { expect } from 'chai';
+import u from '../lib';
+
+describe('u.ifElse', () => {
+  it('does updates with the else if the predicate is false', () => {
+    const object = { a: 0 };
+    const result = u.ifElse(false, { b: 1 }, { b: 2 }, object);
+    expect(result).to.eql({ a: 0, b: 2 });
+  });
+
+  it('updates with the true update if the predicate is true', () => {
+    const object = { a: 0 };
+    const result = u.ifElse(true, { b: 1 }, { b: 4 }, object);
+    expect(result).to.eql({ a: 0, b: 1 });
+  });
+
+  it('will use the result of a function passed as a predicate', () => {
+    const object = { a: 0 };
+    const aIsThree = x => x.a === 3;
+    const result = u.ifElse(aIsThree, { b: 1 }, { b: 4 }, object);
+
+    expect(result).to.eql({ a: 0, b: 4 });
+  });
+
+  it('can be partially applied', () => {
+    const object = { a: 2 };
+    const isEven = x => x % 2 === 0;
+    const inc = x => x + 1;
+    const dec = x => x - 1;
+
+    const result = u({
+      a: u.ifElse(isEven, inc, dec),
+    }, object);
+
+    expect(result).to.eql({ a: 3 });
+  });
+
+  it('freezes the result', () => {
+    expect(Object.isFrozen(u.ifElse(true, {}, {}, {}))).to.be.true;
+    expect(Object.isFrozen(u.ifElse(false, {}, {}, {}))).to.be.true;
+  });
+});