feat(Typescript): Add isType type guard

stencila · Jul 31, 2019 · ed8fb4a · ed8fb4a
1 parent 9096d5f
commit ed8fb4a
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Showing 2 changed files with 49 additions and 12 deletions.
diff --git a/ts/util/__tests__/guards.test.ts b/ts/util/__tests__/guards.test.ts
@@ -8,7 +8,8 @@ import {
   isPrimitive,
   typeIs,
   nodeIs,
-  isa
+  isA,
+  isType
 } from '../guards'
 
 const primitives = [null, true, false, NaN, 2, 'string']
@@ -56,28 +57,47 @@ describe('nodeIs', () => {
     expect(nodeIs(typeMap)({ type: typeMap.someType })).toBe(true))
 })
 
-describe('isa', () => {
+describe('isA', () => {
   const person = { type: 'Person' }
   const para = { type: 'Paragraph', content: [] }
 
   test('it returns false for undefined types', () => {
     // This is a compile error too
     // @ts-ignore
-    expect(isa(person, 'Foo')).toBe(false)
+    expect(isA(person, 'Foo')).toBe(false)
   })
 
   test('it returns true for the right type', () => {
-    expect(isa(person, 'Person')).toBe(true)
-    expect(isa(para, 'Paragraph')).toBe(true)
+    expect(isA(person, 'Person')).toBe(true)
+    expect(isA(para, 'Paragraph')).toBe(true)
   })
 
   test('it returns false for the wrong type', () => {
-    expect(isa(para, 'Person')).toBe(false)
-    expect(isa(null, 'Person')).toBe(false)
-    expect(isa(true, 'Person')).toBe(false)
-    expect(isa(1.0, 'Person')).toBe(false)
-    expect(isa([], 'Person')).toBe(false)
-    expect(isa({ type: 'Foo' }, 'Person')).toBe(false)
+    expect(isA(para, 'Person')).toBe(false)
+    expect(isA(null, 'Person')).toBe(false)
+    expect(isA(true, 'Person')).toBe(false)
+    expect(isA(1.0, 'Person')).toBe(false)
+    expect(isA([], 'Person')).toBe(false)
+    expect(isA({ type: 'Foo' }, 'Person')).toBe(false)
+  })
+})
+
+describe('isType', () => {
+  const person = { type: 'Person' }
+  const para = { type: 'Paragraph', content: [] }
+
+  test('it returns false for undefined types', () => {
+    // This is a compile error too
+    // @ts-ignore
+    expect(isType('Foo')(person)).toBe(false)
+  })
+
+  test('it returns true for the right type', () => {
+    expect(isType('Person')(person)).toBe(true)
+  })
+
+  test('it returns false for the wrong type', () => {
+    expect(isType('Person')(para)).toBe(false)
   })
 })
 

diff --git a/ts/util/guards.ts b/ts/util/guards.ts
@@ -65,10 +65,12 @@ export const is = <Ts extends Entity>(type: keyof TypeMap<Ts>) => {
 }
 
 /**
- * A type guard to determine whether a node is of a particular type.
+ * A type guard to determine whether a node is of a specific type.
  * Returns a boolean value and narrows the TypeScript inferred type to
  * the type.
  *
+ * e.g. `isA(node, 'Paragraph')`
+ *
  * @param type The type to test for
  */
 export const isA = <K extends keyof Types>(
@@ -78,6 +80,21 @@ export const isA = <K extends keyof Types>(
   return isEntity(node) && node.type === type
 }
 
+/**
+ * Returns a type guard to determine whether a node is of a specific type.
+ * Returns a boolean value and narrows the TypeScript inferred type to
+ * the type.
+ *
+ * e.g. `article.content.filter(isType('Paragraph'))`
+ *
+ * @param type The type to test for
+ */
+export const isType = <K extends keyof Types>(type: K) => (
+  node?: Node
+): node is Types[K] => {
+  return node !== undefined && isA(node, type)
+}
+
 /**
  * Type guard to determine whether a node is a primitive type.
  * Returns a boolean value and narrows the TypeScript inferred type.