Add compact and difference functions

Author: sudheerj

src/javascript/algorithms/misc/lodash/compact/compact.js

@@ -0,0 +1,19 @@
+function compact1(arr){
+    return arr.filter(Boolean)
+}
+
+function compact2(arr){
+    let compactArr = [];
+
+    for (let i = 0; i < arr.length; i++) {
+        if(arr[i]) {
+            compactArr.push(arr[i]);
+        }
+    }
+
+    return compactArr;
+}
+
+const arr1 =[1, 'hi', false, 0, 'a', null, undefined, NaN, {}, [], () => {}, ''];
+console.log(compact1(arr1));
+console.log(compact2(arr1));

src/javascript/algorithms/misc/lodash/difference/difference.js

@@ -0,0 +1,41 @@
+function difference1(arr1, arr2){
+    if(arr1.length === 0) return [];
+    if(arr2.length === 0) return arr1;
+
+    return arr1.filter(val => !arr2.includes(val));
+}
+
+function difference2(arr1, arr2){
+    if(arr1.length === 0) return [];
+    if(arr2.length === 0) return arr1;
+
+    const excludeSet = new Set(arr2);
+
+    return arr1.filter(val => !excludeSet.has(val));
+}
+
+function difference3(arr1, arr2){
+    if(arr1.length === 0) return [];
+    if(arr2.length === 0) return arr1;
+
+    const excludeSet = new Set(arr2);
+    let result = [];
+
+    for (let i = 0; i < arr1.length; i++) {
+        const value = arr1[i];
+        if(!excludeSet.has(value) && ! (value === undefined && !(i in arr1))) {
+            result.push(arr1[i]);
+        }
+    }
+
+    return result;
+}
+
+const arr1 = [1, 2, 2, 3, 2], arr2 = [2];
+const arr3 = [1, 2, 3], arr4 = [];
+const arr5 = [], arr6 = [];
+console.log(difference1(arr1, arr2));
+console.log(difference2(arr1, arr2));
+console.log(difference3(arr1, arr2));
+console.log(difference1(arr3, arr4));
+console.log(difference1(arr5, arr6));