feat: where filter, working on #118

doc: https://shopify.github.io/liquid/filters/where/
ruby impl: https://github.com/Shopify/liquid/blob/14cd011cb5eef042af192ad5294c8f0e1ae89f06/lib/liquid/standardfilters.rb

src/builtin/filters/array.ts

@@ -1,4 +1,5 @@
 import { last } from '../../util/underscore'
+import { isTruthy } from '../../render/syntax'
 
 export default {
   'join': (v: any[], arg: string) => v.join(arg === undefined ? ' ' : arg),
@@ -20,5 +21,8 @@ export default {
       u[String(val)] = true
       return true
     })
+  },
+  'where': function<T> (arr: T[], property: string, value?: any): T[] {
+    return arr.filter(obj => value === undefined ? isTruthy(obj[property]) : obj[property] === value)
   }
 }

test/integration/builtin/filters/array.ts

@@ -64,4 +64,28 @@ describe('filters/array', function () {
       return test('{{"" | uniq | join: ","}}', '')
     })
   })
+  describe('where', function () {
+    it('should support filter by property value', function () {
+      return test(`{% assign kitchen_products = products | where: "type", "kitchen" %}
+Kitchen products:
+{% for product in kitchen_products -%}
+- {{ product.title }}
+{% endfor %}`, `
+Kitchen products:
+- Spatula
+- Garlic press
+`)
+    })
+    it('should support filter truthy property', function () {
+      return test(`{% assign available_products = products | where: "available" %}
+Available products:
+{% for product in available_products -%}
+- {{ product.title }}
+{% endfor %}`, `
+Available products:
+- Coffee mug
+- Boring sneakers
+`)
+    })
+  })
 })

test/stub/render.ts

@@ -9,7 +9,16 @@ export const ctx = {
   arr: [-2, 'a'],
   obj: { foo: 'bar' },
   func: function () {},
-  posts: [{ category: 'foo' }, { category: 'bar' }]
+  posts: [{ category: 'foo' }, { category: 'bar' }],
+  products: [
+    {title: 'Vacuum', type: 'living room'},
+    {title: 'Spatula', type: 'kitchen'},
+    {title: 'Television', type: 'living room'},
+    {title: 'Garlic press', type: 'kitchen'},
+    {title: 'Coffee mug', available: true},
+    {title: 'Limited edition sneakers', available: false},
+    {title: 'Boring sneakers', available: true}
+  ]
 }
 
 export async function test (src: string, dst: string) {