diff --git a/String/CheckFlatCase.js b/String/CheckFlatCase.js
index 709825edd1..5f8a332999 100644
--- a/String/CheckFlatCase.js
+++ b/String/CheckFlatCase.js
@@ -12,7 +12,7 @@
 const checkFlatCase = (varname) => {
   // firstly, check that input is a string or not.
   if (typeof varname !== 'string') {
-    return new TypeError('Argument is not a string.')
+    throw new TypeError('Argument is not a string.')
   }
 
   const pat = /^[a-z]*$/
diff --git a/String/CheckKebabCase.js b/String/CheckKebabCase.js
index 6e79ba6a5e..52d322f921 100644
--- a/String/CheckKebabCase.js
+++ b/String/CheckKebabCase.js
@@ -10,7 +10,7 @@
 const CheckKebabCase = (varName) => {
   // firstly, check that input is a string or not.
   if (typeof varName !== 'string') {
-    return new TypeError('Argument is not a string.')
+    throw new TypeError('Argument is not a string.')
   }
 
   const pat = /(\w+)-(\w)([\w-]*)/
diff --git a/String/CheckPascalCase.js b/String/CheckPascalCase.js
index 2e4c1ff3fa..71aaa26770 100644
--- a/String/CheckPascalCase.js
+++ b/String/CheckPascalCase.js
@@ -10,7 +10,7 @@
 const CheckPascalCase = (VarName) => {
   // firstly, check that input is a string or not.
   if (typeof VarName !== 'string') {
-    return new TypeError('Argument is not a string.')
+    throw new TypeError('Argument is not a string.')
   }
 
   const pat = /^[A-Z][A-Za-z]*$/
diff --git a/String/test/CheckCamelCase.test.js b/String/test/CheckCamelCase.test.js
index c1e2d83005..5875e0cd10 100644
--- a/String/test/CheckCamelCase.test.js
+++ b/String/test/CheckCamelCase.test.js
@@ -15,4 +15,8 @@ describe('checkCamelCase', () => {
     const result = checkCamelCase(value)
     expect(result).toBe(false)
   })
+
+  it('should throw when input is not a string', () => {
+    expect(() => checkCamelCase(100)).toThrowError()
+  })
 })
diff --git a/String/test/CheckFlatCase.test.js b/String/test/CheckFlatCase.test.js
index 0277f7c0e1..ccac811bf6 100644
--- a/String/test/CheckFlatCase.test.js
+++ b/String/test/CheckFlatCase.test.js
@@ -15,4 +15,8 @@ describe('checkFlatCase function', () => {
     const actual = checkFlatCase('abcdefghijklmnopqrstuvwxyz')
     expect(actual).toBe(true)
   })
+
+  it('should throw when input is not a string', () => {
+    expect(() => checkFlatCase(100)).toThrowError()
+  })
 })
diff --git a/String/test/CheckKebabCase.test.js b/String/test/CheckKebabCase.test.js
index 45bc5f2d52..239d91674e 100644
--- a/String/test/CheckKebabCase.test.js
+++ b/String/test/CheckKebabCase.test.js
@@ -11,3 +11,7 @@ test('CheckKebabCase(The Algorithms) -> false', () => {
   const res = CheckKebabCase(word)
   expect(res).toBeFalsy()
 })
+
+test('CheckKebabCase throws when input is not a string', () => {
+  expect(() => CheckKebabCase(100)).toThrowError()
+})
diff --git a/String/test/CheckPascalCase.test.js b/String/test/CheckPascalCase.test.js
index 2587023f79..139b66844b 100644
--- a/String/test/CheckPascalCase.test.js
+++ b/String/test/CheckPascalCase.test.js
@@ -17,3 +17,7 @@ test('CheckPascalCase(The Algorithms) -> false', () => {
   const res = CheckPascalCase(word)
   expect(res).toBeFalsy()
 })
+
+test('CheckPascalCase throws when input is not a string', () => {
+  expect(() => CheckPascalCase(100)).toThrowError()
+})