Add u.is

CHANGELOG.md

@@ -1,9 +1,10 @@
 # Change Log
 
 ## [unreleased]
+* Add `u.is` to test predicates in a single path. (https://github.com/substantial/updeep/issues/13)
 
 ## [0.4.0]
-* Add `u.if` and `u.ifElse` to conditionally update objects.
+* Add `u.if` and `u.ifElse` to conditionally update objects. (https://github.com/substantial/updeep/issues/12)
 * 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

@@ -219,8 +219,8 @@ u({ x: u.omit(['b', 'c']) }, { x: { a: 0, b: 0, c: 0 } });
 Reject items from an array. See [`_.reject`](https://lodash.com/docs#reject).
 
 ```js
-function even(i) { return i % 2 === 0 };
-u({ x: u.reject(even) }, { x: [1, 2, 3, 4] });
+function isEven(i) { return i % 2 === 0; }
+u({ x: u.reject(isEven) }, { x: [1, 2, 3, 4] });
 // => { x: [1, 3] }
 ```
 
@@ -235,6 +235,29 @@ u({ x: u.withDefault([], { 0: 3 }) }, {});
 
 See the [tests] for more examples.
 
+### `u.is(path(, predicate)(, object))`
+
+Returns `true` if the `predicate` matches the `path` applied to the `object`.
+If the `predicate` is a function, the result is returned. If not, they are compared with `===`.
+
+```js
+u.is('a.b', 4, { a: { b: 4 } });
+// => true
+```
+
+```js
+function isEven(i) { return i % 2 === 0; }
+u.is('a.b', isEven, { a: { b: 4 } });
+// => true
+```
+
+```js
+u({
+  person: u.if(u.is('name.first', 'Jen'), u.in('name.last', 'Simpson'))
+}, { person: { name: { first: 'Jen', last: 'Matthews' } } });
+// => { person: { name: { first: 'Jen', last: 'Simpson' } } }
+```
+
 ## Install
 
 ```sh

lib/in.js

@@ -1,12 +1,9 @@
 import curry from 'lodash/function/curry';
-import reject from 'lodash/collection/reject';
 import update from './update';
+import splitPath from './util/splitPath';
 
 function updateIn(path, value, object) {
-  const parts = Array.isArray(path) ?
-    path :
-    reject(path.split('.'), x => !x);
-
+  const parts = splitPath(path);
   const updates = parts.reduceRight((acc, key) => ({ [key]: acc }), value);
 
   return update(updates, object);

lib/index.js

@@ -1,5 +1,6 @@
 import freeze from './freeze';
 import _in from './in';
+import is from './is';
 import ifElse from './ifElse';
 import map from './map';
 import omit from './omit';
@@ -14,6 +15,7 @@ const u = update;
 u.if = ifElse(_, _, {});
 u.ifElse = ifElse;
 u.in = _in;
+u.is = is;
 u.freeze = freeze;
 u.map = map;
 u.omit = omit;

lib/is.js

@@ -0,0 +1,21 @@
+import splitPath from './util/splitPath';
+import curry from 'lodash/function/curry';
+
+function is(path, predicate, object) {
+  const parts = splitPath(path);
+
+  let rest = object;
+  let part;
+  for (part of parts) {
+    if (typeof rest === 'undefined') return false;
+    rest = rest[part];
+  }
+
+  if (typeof predicate === 'function') {
+    return predicate(rest);
+  }
+
+  return predicate === rest;
+}
+
+export default curry(is);

lib/util/splitPath.js

@@ -0,0 +1,7 @@
+import reject from 'lodash/collection/reject';
+
+export default function splitPath(path) {
+  return Array.isArray(path) ?
+    path :
+    reject(path.split('.'), x => !x);
+}

test/is-spec.js

@@ -0,0 +1,59 @@
+import { expect } from 'chai';
+import u from '../lib';
+
+describe('u.is', () => {
+  it('returns true if path matches a value predicate', () => {
+    const result = u.is('a.b', 4, { a: { b: 4 } });
+    expect(result).to.be.true;
+  });
+
+  it('returns true if path matches a function predicate', () => {
+    const isEven = x => x % 2 === 0;
+    const result = u.is('a.b', isEven, { a: { b: 6 } });
+    expect(result).to.be.true;
+  });
+
+  it('returns false if path matches a value predicate', () => {
+    const result = u.is('a.b', 4, { a: { b: 5 } });
+    expect(result).to.be.false;
+  });
+
+  it('returns false if path matches a function predicate', () => {
+    const isEven = x => x % 2 === 0;
+    const result = u.is('a.b', isEven, { a: { b: 7 } });
+    expect(result).to.be.false;
+  });
+
+  it('returns false if the path does not exist', () => {
+    const result = u.is('a.b.c.d', 4, { a: { b: {} } });
+    expect(result).to.be.false;
+  });
+
+  it('can test for undefined', () => {
+    const result = u.is('a.b.c', undefined, { a: { b: {} } });
+    expect(result).to.be.true;
+  });
+
+  it('tests the actual object if a blank path is given', () => {
+    const result = u.is('', 4, 4);
+    expect(result).to.be.true;
+  });
+
+  it('can use arrays as paths', () => {
+    const result = u.is(['a', 'b'], 4, { a: { b: 4 } });
+    expect(result).to.be.true;
+  });
+
+  it('can include array indexes in paths', () => {
+    let result = u.is('a.1.b', 4, { a: [{}, { b: 4 }] });
+    expect(result).to.be.true;
+
+    result = u.is(['a', 1, 'b'], 4, { a: [{}, { b: 4 }] });
+    expect(result).to.be.true;
+  });
+
+  it('can be partially applied', () => {
+    const result = u.is('a.b')(4)({ a: { b: 4 } });
+    expect(result).to.be.true;
+  });
+});