add gradient filter

Author: lukasoppermann

src/filters/index.ts

@@ -7,6 +7,7 @@ export {isDuration} from './isDuration.js'
 export {isFromFile} from './isFromFile.js'
 export {isFontFamily} from './isFontFamily.js'
 export {isFontWeight} from './isFontWeight.js'
+export {isGradient} from './isGradient.js'
 export {isNumber} from './isNumber.js'
 export {isShadow} from './isShadow.js'
 export {isSource} from './isSource.js'

src/filters/isGradient.test.ts

@@ -0,0 +1,22 @@
+import {getMockToken} from '../test-utilities/index.js'
+import {isGradient} from './isGradient.js'
+
+describe('Filter: isGradient', () => {
+  it('returns true if $type property is `color`', () => {
+    expect(isGradient(getMockToken({$type: 'gradient'}))).toStrictEqual(true)
+  })
+
+  it('returns false if $type property is not `color`', () => {
+    expect(isGradient(getMockToken({$type: 'pumpkin'}))).toStrictEqual(false)
+  })
+
+  it('returns false if $type property is missing', () => {
+    expect(isGradient(getMockToken({alpha: 0.4}))).toStrictEqual(false)
+  })
+
+  it('returns false if $type property is falsy', () => {
+    expect(isGradient(getMockToken({$type: false}))).toStrictEqual(false)
+    expect(isGradient(getMockToken({$type: undefined}))).toStrictEqual(false)
+    expect(isGradient(getMockToken({$type: null}))).toStrictEqual(false)
+  })
+})

src/filters/isGradient.ts

@@ -0,0 +1,11 @@
+import type {TransformedToken} from 'style-dictionary/types'
+
+/**
+ * @description Checks if token is of $type `gradient`
+ * @param token [TransformedToken](https://github.com/amzn/style-dictionary/blob/main/types/TransformedToken.d.ts)
+ * @returns boolean
+ */
+export const isGradient = (token: TransformedToken): boolean => {
+  const typeValue = token.$type ?? token.type
+  return typeValue === 'gradient'
+}