Ignore undefined props

src/index.ts

@@ -28,6 +28,12 @@ export function renderString(
 
     const variableValue = props[variable]
 
+    // If the variable doesn't exist, do not process the template 
+    if (variableValue === undefined) {
+      expressions[i] = `${delimiters[0]}${expressions[i]}${delimiters[1]}`
+      continue
+    }
+
     expressions[i] = filters.reduce((variableValue, filter) => {
       const splitPattern = /:(?![^{}]*})/g
       const [filterMethod, args] = filter.split(splitPattern)

tests/index.test.ts

@@ -106,11 +106,22 @@ describe('renderString', () => {
       expect(renderString('Test {{ value }}', { value: 123 })).toBe('Test 123')
     })
 
-    test('should return ignore invalid filters', () => {
+    test('should ignore invalid filters', () => {
       expect(renderString('{{ value | invalidFilter }}', { value: 123 })).toBe(
         123
       )
     })
+
+    test('should ignore undefined props', () => {
+      expect(renderString(
+        '{{ prefix }}/{{ suffix }}',
+        { prefix: 'abc' }
+      )).toBe('abc/{{ suffix }}')
+      expect(renderString(
+        '{{ prefix }}/{{ suffix | upcase }}',
+        { prefix: 'abc' }
+      )).toBe('abc/{{ suffix | upcase }}')
+    })
   })
 })
 
@@ -135,4 +146,11 @@ describe('renderObject', () => {
       list: [1, 1234, 3],
     })
   })
+
+  test('should ignore undefined props', () => {
+    expect(renderObject(
+      { key: '{{ nested.prefix }}/{{ nested.suffix }}' },
+      { nested: { prefix: 'abc' } }
+    )).toEqual({ key: 'abc/{{ nested.suffix }}' })
+  })
 })