diff --git a/students/devendra-katwal/ex1.js b/students/devendra-katwal/ex1.js
new file mode 100644
index 0000000..d7c64cc
--- /dev/null
+++ b/students/devendra-katwal/ex1.js
@@ -0,0 +1,15 @@
+/*
+Write a JavaScript function to check whether an input is an array or not.
+
+Test Data :
+console.log(isArray('w3resource')); // false
+console.log(isArray([1, 2, 4, 0])); // true
+*/
+
+
+
+function isArray(input){
+    return Array.isArray(input);
+}
+console.log(isArray('w3resource')); // false
+console.log(isArray([1, 2, 4, 0])); // true
\ No newline at end of file
diff --git a/students/devendra-katwal/ex2.js b/students/devendra-katwal/ex2.js
new file mode 100644
index 0000000..0f14140
--- /dev/null
+++ b/students/devendra-katwal/ex2.js
@@ -0,0 +1,29 @@
+/* 
+Write a JavaScript function to get the first element of an array. Passing a parameter 'n' will return the first 'n' elements of the array.
+
+Test Data : 
+console.log(first([7, 9, 0, -2])); // 7
+console.log(first([],3)); // []
+console.log(first([7, 9, 0, -2],3)); // [7,9,0]
+console.log(first([7, 9, 0, -2],6)); // [7, 9, 0, -2]
+console.log(first([7, 9, 0, -2],-3)); // [] 
+
+*/
+
+function first(arr, n){
+    if(arr.length === 0){
+        return [];
+    }else if (arguments.length>1){
+        return arr.splice(0,n);
+    }else if (arr.length ===1){
+        return arr;
+    }else if (n === null || n === 'undefined'){
+        return arr[0];
+    }
+}
+console.log(first([7, 9, 0, -2])); // 7
+console.log(first([],3)); // []
+console.log(first([7, 9, 0, -2],3)); // [7,9,0]
+console.log(first([7, 9, 0, -2],6)); // [7, 9, 0, -2]
+console.log(first([7, 9, 0, -2],-3)); // [] 
+console.log(first([7, 9, 0, -2],'undefined')); // [] 
\ No newline at end of file
diff --git a/students/devendra-katwal/ex3.js b/students/devendra-katwal/ex3.js
new file mode 100644
index 0000000..6a90f05
--- /dev/null
+++ b/students/devendra-katwal/ex3.js
@@ -0,0 +1,15 @@
+/*
+Write a simple JavaScript program to join all elements of the following array into a string.
+
+Sample array : 
+var myText = ['This', 'is', 'not', 'working'];
+joinArray(myText);
+
+Expected Output : 
+This is not working
+*/
+function joinArray(myText){
+    return myText.join(' ')
+}
+
+console.log(joinArray(['This', 'is', 'not', 'working']));
\ No newline at end of file
diff --git a/students/devendra-katwal/ex4.js b/students/devendra-katwal/ex4.js
new file mode 100644
index 0000000..1585ddb
--- /dev/null
+++ b/students/devendra-katwal/ex4.js
@@ -0,0 +1,25 @@
+/* 
+ATM machines allow 4 or 6 digit PIN codes and PIN codes cannot contain anything but exactly 4 digits 
+or exactly 6 digits. If the function is passed a valid PIN string, return true, else return false. 
+
+validatePIN(1234); // false
+validatePIN(00004324); // false
+validatePIN('2312'); // true
+validatePin('asd123'); // false
+validatePin('000010'); // true
+*/
+function validatePIN(input){
+    if(input.length === 4 || input.length === 6 && !isNaN(input)){
+        return true
+    }else {
+        return false
+    }
+}
+
+console.log(validatePIN(1234)); // false
+console.log(validatePIN(00004324)); // false
+console.log(validatePIN('2312')); // true
+console.log(validatePIN('asd123')); // false
+console.log(validatePIN('000010')); // true
+
+
diff --git a/students/hoang-pham/copy-and-rename/ex1.js b/students/hoang-pham/copy-and-rename/ex1.js
new file mode 100644
index 0000000..1c7fc89
--- /dev/null
+++ b/students/hoang-pham/copy-and-rename/ex1.js
@@ -0,0 +1,9 @@
+/*
+Write a JavaScript function to check whether an input is an array or not.
+
+Test Data :
+console.log(isArray('w3resource')); // false
+console.log(isArray([1, 2, 4, 0])); // true
+*/
+
+
diff --git a/students/hoang-pham/copy-and-rename/ex2.js b/students/hoang-pham/copy-and-rename/ex2.js
new file mode 100644
index 0000000..eb24fa7
--- /dev/null
+++ b/students/hoang-pham/copy-and-rename/ex2.js
@@ -0,0 +1,11 @@
+/* 
+Write a JavaScript function to get the first element of an array. Passing a parameter 'n' will return the first 'n' elements of the array.
+
+Test Data : 
+console.log(first([7, 9, 0, -2])); // 7
+console.log(first([],3)); // []
+console.log(first([7, 9, 0, -2],3)); // [7,9,0]
+console.log(first([7, 9, 0, -2],6)); // [7, 9, 0, -2]
+console.log(first([7, 9, 0, -2],-3)); // [] 
+
+*/
\ No newline at end of file
diff --git a/students/hoang-pham/copy-and-rename/ex3.js b/students/hoang-pham/copy-and-rename/ex3.js
new file mode 100644
index 0000000..eb98a2a
--- /dev/null
+++ b/students/hoang-pham/copy-and-rename/ex3.js
@@ -0,0 +1,10 @@
+/*
+Write a simple JavaScript program to join all elements of the following array into a string.
+
+Sample array : 
+var myText = ['This', 'is', 'not', 'working'];
+joinArray(myText);
+
+Expected Output : 
+This is not working
+ */
\ No newline at end of file
diff --git a/students/hoang-pham/copy-and-rename/ex4.js b/students/hoang-pham/copy-and-rename/ex4.js
new file mode 100644
index 0000000..72f98cc
--- /dev/null
+++ b/students/hoang-pham/copy-and-rename/ex4.js
@@ -0,0 +1,9 @@
+/* 
+ATM machines allow 4 or 6 digit PIN codes and PIN codes cannot contain anything but exactly 4 digits or exactly 6 digits. If the function is passed a valid PIN string, return true, else return false. 
+
+validatePIN(1234); // false
+validatePIN(00004324); // false
+validatePIN('2312'); // true
+validatePin('asd123'); // false
+validatePin('000010'); // true
+ */
\ No newline at end of file