diff --git a/.eslintignore b/.eslintignore
new file mode 100644
index 0000000..f77a02d
--- /dev/null
+++ b/.eslintignore
@@ -0,0 +1,4 @@
+node_modules
+dist
+**/*/*.d.ts
+./*js
diff --git a/.eslintrc b/.eslintrc
new file mode 100644
index 0000000..11643ef
--- /dev/null
+++ b/.eslintrc
@@ -0,0 +1,12 @@
+{
+  "root": true,
+  "parser": "@typescript-eslint/parser",
+  "plugins": [
+    "@typescript-eslint"
+  ],
+  "extends": [
+    "eslint:recommended",
+    "plugin:@typescript-eslint/eslint-recommended",
+    "plugin:@typescript-eslint/recommended"
+  ]
+}
diff --git a/jest.config.js b/jest.config.js
index f498143..da2ee0d 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -188,5 +188,5 @@ module.exports = {
   // watchPathIgnorePatterns: [],
 
   // Whether to use watchman for file crawling
-  // watchman: true,
+  // watchman: true
 };
diff --git a/package.json b/package.json
index 7dd6de5..4147237 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "datapipe-js",
-  "version": "0.2.7",
+  "version": "0.2.8",
   "description": "dataPipe is a JavaScript library for data manipulations, data transformations and data wrangling library inspired by LINQ (C#) and Pandas (Python)",
   "main": "dist/data-pipe.min.js",
   "module": "dist/data-pipe.esm.js",
@@ -20,7 +20,9 @@
     "docs": "npx typedoc src --plugin none",
     "docs:md": "npx typedoc src --out md-docs --plugin typedoc-plugin-markdown",
     "deploy": "npm run docs && npx gh-pages -d docs",
-    "dev": "npx rollup --config rollup.config.dev.js --watch"
+    "dev": "npx rollup --config rollup.config.dev.js --watch",
+    "lint": "eslint . --ext .ts",
+    "lint-fix": "eslint . --ext .ts --fix"
   },
   "repository": {
     "type": "git",
@@ -48,6 +50,9 @@
   ],
   "devDependencies": {
     "@types/jest": "^24.9.1",
+    "@typescript-eslint/eslint-plugin": "^2.24.0",
+    "@typescript-eslint/parser": "^2.24.0",
+    "eslint": "^6.8.0",
     "jest": "^24.9.0",
     "jest-fetch-mock": "^2.1.2",
     "rollup": "^1.31.1",
@@ -57,8 +62,8 @@
     "rollup-plugin-typescript2": "^0.25.3",
     "rollup-plugin-uglify": "^6.0.4",
     "ts-jest": "^24.3.0",
-    "typedoc": "^0.15.8",
-    "typedoc-plugin-markdown": "^2.2.16",
-    "typescript": "^3.7.5"
+    "typedoc": "^0.17.3",
+    "typedoc-plugin-markdown": "^2.2.17",
+    "typescript": "^3.8.3"
   }
 }
diff --git a/src/array/joins.ts b/src/array/joins.ts
index bf9ea81..c60f6ba 100644
--- a/src/array/joins.ts
+++ b/src/array/joins.ts
@@ -63,17 +63,17 @@ export function fullJoin(
     // build a lookup maps for both arrays.
     // so, both of them have to be unique, otherwise it will flattern result
     const leftArrayMap = Object.create(null);
-    for (let item of rightArray) {
+    for (const item of rightArray) {
         leftArrayMap[leftKeySelector(item)] = item;
     }
 
     const rightArrayMap = Object.create(null);
-    for (let item of rightArray) {
+    for (const item of rightArray) {
         rightArrayMap[rightKeySelector(item)] = item;
     }
 
     const result: any[] = [];
-    for (let leftItem of leftArray) {
+    for (const leftItem of leftArray) {
         const leftKey = leftKeySelector(leftItem);
         const rightItem = rightArrayMap[leftKey] || null;
 
@@ -87,7 +87,7 @@ export function fullJoin(
     }
 
     // add remaining right items
-    for (let rightItemKey in rightArrayMap) {
+    for (const rightItemKey in rightArrayMap) {
         const rightItem = rightArrayMap[rightItemKey];
         const resultItem = resultSelector(null, rightItem);
 
@@ -119,16 +119,16 @@ export function merge(
     // build a lookup maps for both arrays.
     // so, both of them have to be unique, otherwise it will flattern result
     const targetArrayMap = Object.create(null);
-    for (let item of sourceArray) {
+    for (const item of sourceArray) {
         targetArrayMap[targetKeySelector(item)] = item;
     }
 
     const sourceArrayMap = Object.create(null);
-    for (let item of sourceArray) {
+    for (const item of sourceArray) {
         sourceArrayMap[sourceKeySelector(item)] = item;
     }
 
-    for (let sourceItemKey of Object.keys(sourceArrayMap)) {
+    for (const sourceItemKey of Object.keys(sourceArrayMap)) {
         const sourceItem = sourceArrayMap[sourceItemKey];
         if (!targetArrayMap[sourceItemKey]) {
             targetArray.push(sourceItem);
@@ -184,12 +184,12 @@ function leftOrInnerJoin(
 
     // build a lookup map
     const rightArrayMap = Object.create(null);
-    for (let item of rightArray) {
+    for (const item of rightArray) {
         rightArrayMap[rightKeySelector(item)] = item;
     }
 
     const result: any[] = [];
-    for (let leftItem of leftArray) {
+    for (const leftItem of leftArray) {
         const leftKey = leftKeySelector(leftItem);
         const rightItem = rightArrayMap[leftKey] || null;
 
diff --git a/src/array/stats.ts b/src/array/stats.ts
index d0feeed..5a1c12b 100644
--- a/src/array/stats.ts
+++ b/src/array/stats.ts
@@ -14,11 +14,11 @@ import { isArrayEmptyOrNull } from "./utils";
  * sum([{ val: 1 }, { val: 5 }], i => i.val); // 6
  */
 export function sum(array: any[], field?: Selector | string): number | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   const elementSelector = fieldSelector(field);
 
-  let sum: number = 0;
+  let sum = 0;
   for (const item of array) {
     const numberVal = parseNumber(item, elementSelector);
     if (numberVal) {
@@ -38,7 +38,7 @@ export function sum(array: any[], field?: Selector | string): number | null {
  * avg([1, 5, 3]); // 3
  */
 export function avg(array: any[], field?: Selector | string): number | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   const elementSelector = fieldSelector(field);
 
@@ -73,7 +73,7 @@ export function min(array: any[], field?: Selector | string): number | Date | nu
 export function max(array: any[], field?: Selector | string): number | Date | null {
   const elementSelector = fieldSelector(field);
   const numberArray = getNumberValuesArray(array, elementSelector);
-  if (isArrayEmptyOrNull(numberArray)) { return null };
+  if (isArrayEmptyOrNull(numberArray)) { return null }
   const max = Math.max(...numberArray);
   const item = elementSelector ? elementSelector(array[0]) : array[0];
   if (item instanceof Date) {
@@ -103,7 +103,7 @@ export function count(array: any[], predicate?: Predicate): number | null {
  * @param predicate Predicate function invoked per iteration.
  */
 export function first<T = any>(array: T[], predicate?: Predicate): T | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   if (!predicate) {
     return array[0];
@@ -122,7 +122,7 @@ export function first<T = any>(array: T[], predicate?: Predicate): T | null {
  * @param predicate Predicate function invoked per iteration.
  */
 export function last<T = any>(array: T[], predicate?: Predicate): T | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   let lastIndex = array.length - 1;
   if (!predicate) {
@@ -144,7 +144,7 @@ export function last<T = any>(array: T[], predicate?: Predicate): T | null {
  * @param elementSelector Function invoked per iteration.
  */
 export function countBy(array: any[], elementSelector: Selector): { [key: string]: number } {
-  if (!array || !Array.isArray(array)) { throw Error('No array provided') };
+  if (!array || !Array.isArray(array)) { throw Error('No array provided') }
 
   const results: { [key: string]: number } = {};
   const length = array.length;
@@ -165,7 +165,7 @@ export function countBy(array: any[], elementSelector: Selector): { [key: string
  * @param field Property name or Selector function invoked per iteration.
  */
 export function mean(array: any[], field?: Selector | string): number | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   let res = 0;
   for (let i = 0, c = 0, len = array.length; i < len; ++i) {
@@ -185,7 +185,7 @@ export function mean(array: any[], field?: Selector | string): number | null {
  * @param p quantile.
  */
 export function quantile(array: any[], p: number, field?: Selector | string): number | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   const len = (array.length - 1) * p + 1;
   const l = Math.floor(len);
@@ -193,7 +193,7 @@ export function quantile(array: any[], p: number, field?: Selector | string): nu
   const val = elementSelector ? elementSelector(array[l - 1]) : array[l - 1];
   const e = len - l;
   return e ? val + e * (array[l] - val) : val;
-};
+}
 
 /**
  * Get sample variance of an array.
@@ -201,7 +201,7 @@ export function quantile(array: any[], p: number, field?: Selector | string): nu
  * @param field Property name or Selector function invoked per iteration.
  */
 export function variance(array: any[], field?: Selector | string): number | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   const elementSelector = fieldSelector(field);
   if (!Array.isArray(array) || array.length < 2) {
@@ -218,7 +218,7 @@ export function variance(array: any[], field?: Selector | string): number | null
   }
   M2 = M2 / (c - 1);
   return M2;
-};
+}
 
 /**
  * Get the sample standard deviation of an array.
@@ -226,14 +226,14 @@ export function variance(array: any[], field?: Selector | string): number | null
  * @param field Property name or Selector function invoked per iteration.
  */
 export function stdev(array: any[], field?: Selector | string): number | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   const varr = variance(array, field);
 
   if (varr === null) { return null; }
 
   return Math.sqrt(varr);
-};
+}
 
 /**
  * Get median of an array.
@@ -241,11 +241,11 @@ export function stdev(array: any[], field?: Selector | string): number | null {
  * @param field Property name or Selector function invoked per iteration.
  */
 export function median(array: any[], field?: Selector | string): number | null {
-  if (isArrayEmptyOrNull(array)) { return null };
+  if (isArrayEmptyOrNull(array)) { return null }
 
   array.sort(fieldComparator(field));
   return quantile(getNumberValuesArray(array, field), 0.5);
-};
+}
 
 function fieldComparator(field?: string | Selector): (a: any, b: any) => number {
   return (a: any, b: any) => {
diff --git a/src/array/transform.ts b/src/array/transform.ts
index e9fa6d7..345c75e 100644
--- a/src/array/transform.ts
+++ b/src/array/transform.ts
@@ -8,7 +8,7 @@ import { sum } from "./stats";
  * @param elementSelector Function invoked per iteration.
  */
 export function groupBy(array: any[], groupByFields: string | string[] | Selector): any[] {
-    if (!Array.isArray(array)) { throw Error('An array is not provided') };
+    if (!Array.isArray(array)) { throw Error('An array is not provided') }
 
     if (!array.length) { return array; }
 
@@ -33,7 +33,7 @@ export function groupBy(array: any[], groupByFields: string | string[] | Selecto
  * flatten([1, 4, [2, [5, 5, [9, 7]], 11], 0]); // length 9
  */
 export function flatten(array: any[]): any[] {
-    if (!Array.isArray(array)) { throw Error('An array is not provided') };
+    if (!Array.isArray(array)) { throw Error('An array is not provided') }
 
     if (!array.length) { return array; }
 
@@ -41,7 +41,7 @@ export function flatten(array: any[]): any[] {
     const length = array.length;
 
     for (let i = 0; i < length; i++) {
-        var value = array[i];
+        const value = array[i];
         if (Array.isArray(value)) {
             res = [...res, ...flatten(value)];
         } else {
@@ -63,7 +63,7 @@ export function flatten(array: any[]): any[] {
 export function pivot(array: any, rowFields: string | string[],columnField: string, dataField: string,
     aggFunction?: (array: any[]) => any | null, columnValues?: string[]): any[] {
 
-    if (!Array.isArray(array)) { throw Error('An array is not provided') };
+    if (!Array.isArray(array)) { throw Error('An array is not provided') }
 
     if (!array.length) { return array; }
     
@@ -90,7 +90,7 @@ export function pivot(array: any, rowFields: string | string[],columnField: stri
         }
     }
 
-    var result: any[] = [];
+    const result: any[] = [];
     for (const groupName of Object.keys(groups)) {
 
         const item = Object.create(null);
@@ -118,7 +118,7 @@ export function pivot(array: any, rowFields: string | string[],columnField: stri
  * @param data 
  */
 export function transpose(data: any[]): any[] {
-    if (!Array.isArray(data)) { throw Error('An array is not provided') };
+    if (!Array.isArray(data)) { throw Error('An array is not provided') }
 
     if (!data.length) { return data; }
   
diff --git a/src/array/utils.ts b/src/array/utils.ts
index 41b6321..c45e8e9 100644
--- a/src/array/utils.ts
+++ b/src/array/utils.ts
@@ -2,7 +2,7 @@ import { parseNumber, parseDatetimeOrNull } from "../utils";
 
 /**
  * Checks if array is empty or null or array at all
- * @param array 
+ * @param array
  */
 export function isArrayEmptyOrNull(array: any[]): boolean {
   return !array || !Array.isArray(array) || !array.length;
@@ -30,13 +30,31 @@ export function sort(array: any[], ...fields: string[]) {
     return {
       asc,
       field: field.replace(asc ? /\sASC$/ : /\sDESC$/, '')
-    }
+    };
   });
 
   array.sort(comparator(sortFields));
   return array;
 }
 
+function compare(a: any, b: any, { field, asc }: any): number {
+  const valA = a[field];
+  const valB = b[field];
+  const order = asc ? 1 : -1;
+
+  if (valA !== undefined && valB === undefined) {
+    return order;
+  }
+
+  switch (typeof valA) {
+    case 'number': return order * compareNumbers(valA, valB);
+    case 'string': return order * compareStrings(valA, valB);
+    case 'object': return order * compareObjects(valA, valB);
+    case 'undefined': return valB === undefined ? 0 : (-1 * order);
+  }
+  return 0;
+}
+
 function comparator(sortFields: any[]) {
   if (sortFields.length) {
     return (a: any, b: any) => {
@@ -48,22 +66,8 @@ function comparator(sortFields: any[]) {
         }
       }
       return 0;
-    }
-  }
-}
-
-function compare(a: any, b: any, { field, asc }: any): number {
-  const valA = a[field];
-  const valB = b[field];
-  const order = asc ? 1 : -1;
-
-  switch (typeof valA) {
-    case 'number': return order * compareNumbers(valA, valB);
-    case 'string': return order * compareStrings(valA, valB);
-    case 'object': return order * compareObjects(valA, valB);
-    case 'undefined': return -1 * order;
+    };
   }
-  return 0;
 }
 
 function compareStrings(a: string, b: any): number {
@@ -72,25 +76,28 @@ function compareStrings(a: string, b: any): number {
 
 function compareNumbers(a: number, b: any): number {
   const bNumVal = parseNumber(b);
-  if (bNumVal == undefined) {
+  if (bNumVal === undefined) {
     return 1;
   }
 
   return a - bNumVal;
 }
 
-function compareObjects(a: any, b: any) {
+function compareObjects(a: any, b: any): number {
   const aDate = parseDatetimeOrNull(a);
+  const bDate = parseDatetimeOrNull(b);
+
+  if (!aDate && !bDate) {
+    return 0;
+  }
+
   if (!aDate) {
-    return -1
+    return -1;
   }
-  const bDate = parseDatetimeOrNull(b);
+
   if (!bDate) {
-    return 1
-  }
-  if (a instanceof Date) {
-    return a.getTime() - bDate.getTime();
+    return 1;
   }
 
-  return -1;
+  return aDate.getTime() - bDate.getTime();
 }
diff --git a/src/string/stringUtils.ts b/src/string/stringUtils.ts
index 9f05309..682a400 100644
--- a/src/string/stringUtils.ts
+++ b/src/string/stringUtils.ts
@@ -1,7 +1,7 @@
-export function formatCamelStr(str: string = ''): string {
+export function formatCamelStr(str = ''): string {
     return str.replace(/^\w/, c => c.toUpperCase()).replace(/([a-z0-9])([A-Z])/g, '$1 $2').replace(/_/g, ' ');
 }
 
-export function replaceAll(text: string, searchValue: string, replaceValue: string = ''): string {
+export function replaceAll(text: string, searchValue: string, replaceValue = ''): string {
     return text.replace(new RegExp(searchValue, 'g'), replaceValue || '');
 }
diff --git a/src/tests/array.spec.ts b/src/tests/array.spec.ts
index 21dbf5e..ad0f1c1 100644
--- a/src/tests/array.spec.ts
+++ b/src/tests/array.spec.ts
@@ -307,27 +307,27 @@ describe('Test array methods', () => {
     // expect(res.filter(r => r.product === 'P2')[0]['2018']).toBe('Data21');
     // expect(res.filter(r => r.product === 'P3')[0]['2019']).toBe('Data33');
     // expect(res.filter(r => r.product === 'P3')[0]['2018']).toBe(null);
-  })
+  });
 
   it('stats quantile for sorted array', () => {
-    const data = [3, 1, 2, 4, 0].sort();
-    expect(quantile(data, 0)).toBe(0);
-    expect(quantile(data, 1 / 4)).toBe(1);
-    expect(quantile(data, 1.5 / 4)).toBe(1.5);
-    expect(quantile(data, 2 / 4)).toBe(2);
-    expect(quantile(data, 2.5 / 4)).toBe(2.5);
-    expect(quantile(data, 3 / 4)).toBe(3);
-    expect(quantile(data, 3.2 / 4)).toBe(3.2);
-    expect(quantile(data, 4 / 4)).toBe(4);
-
-    var even = [3, 6, 7, 8, 8, 10, 13, 15, 16, 20];
+    const numbersData = [3, 1, 2, 4, 0].sort();
+    expect(quantile(numbersData, 0)).toBe(0);
+    expect(quantile(numbersData, 1 / 4)).toBe(1);
+    expect(quantile(numbersData, 1.5 / 4)).toBe(1.5);
+    expect(quantile(numbersData, 2 / 4)).toBe(2);
+    expect(quantile(numbersData, 2.5 / 4)).toBe(2.5);
+    expect(quantile(numbersData, 3 / 4)).toBe(3);
+    expect(quantile(numbersData, 3.2 / 4)).toBe(3.2);
+    expect(quantile(numbersData, 4 / 4)).toBe(4);
+
+    const even = [3, 6, 7, 8, 8, 10, 13, 15, 16, 20];
     expect(quantile(even, 0)).toBe(3);
     expect(quantile(even, 0.25)).toBe(7.25);
     expect(quantile(even, 0.5)).toBe(9);
     expect(quantile(even, 0.75)).toBe(14.5);
     expect(quantile(even, 1)).toBe(20);
 
-    var odd = [3, 6, 7, 8, 8, 9, 10, 13, 15, 16, 20];
+    const odd = [3, 6, 7, 8, 8, 9, 10, 13, 15, 16, 20];
     expect(quantile(odd, 0)).toBe(3);
     expect(quantile(odd, 0.25)).toBe(7.5);
     expect(quantile(odd, 0.5)).toBe(9);
@@ -386,5 +386,15 @@ describe('Test array methods', () => {
     expect(arr[2].name).toBe('Marry');
     arr = pipeFuncs.sort([5, 2, 9, 4]);
     expect(arr[2]).toBe(5);
-  })
-})
+
+    const arrWithUndefinedProps = [
+      { name: 'Tom', age: 7 },
+      { name: 'Bob', age: 10 },
+      { age: 5 },
+      { name: 'Jerry', age: 3 }];
+    arr = pipeFuncs.sort(arrWithUndefinedProps, 'name ASC') || [];
+    expect(arr[0].age).toBe(5);
+    arr = pipeFuncs.sort(arrWithUndefinedProps, 'name DESC') || [];
+    expect(arr[0].age).toBe(7);
+  });
+});
diff --git a/src/tests/dsv-parser.spec.ts b/src/tests/dsv-parser.spec.ts
index 4f8d1c3..195df15 100644
--- a/src/tests/dsv-parser.spec.ts
+++ b/src/tests/dsv-parser.spec.ts
@@ -67,7 +67,7 @@ describe('Dsv Parser specification', () => {
 
   it('skipUntil', () => {
     const csv = ["", " * not Empty *", "F1\tF2\tF3", `1\t1,000.32\t"Test, comma"`].join('\n')
-    var options = new ParsingOptions();
+    const options = new ParsingOptions();
     options.delimiter = '\t';
     options.skipUntil = t => t && t.length > 1;
 
@@ -78,7 +78,7 @@ describe('Dsv Parser specification', () => {
 
   it('empty values', () => {
     const csv = ["", "", , "\t\t\t", "F1\tF2\tF3", `1\t1,000.32\t"Test, comma"`, "\t\t"].join('\n')
-    var options = new ParsingOptions();
+    const options = new ParsingOptions();
     options.delimiter = '\t';
 
     const result = parseCsv(csv, options);
@@ -88,7 +88,7 @@ describe('Dsv Parser specification', () => {
 
   it('Date Fields', () => {
     const csv = ["F1\tF2\tF3", `2020-02-11\t1,000.32\t"Test, comma"`].join('\n')
-    var options = new ParsingOptions();
+    const options = new ParsingOptions();
     options.delimiter = '\t';
     options.dateFields = ['F1']
 
diff --git a/src/types.ts b/src/types.ts
index 8750dd5..c1d23a0 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1,8 +1,8 @@
 export type Predicate<T = any> = (p: T) => boolean;
 export type Selector<T = any, V = any> = (p: T) => V;
 export class ParsingOptions {
-    delimiter: string = ',';
-    skipRows: number = 0;
+    delimiter = ',';
+    skipRows = 0;
     dateFields: string[] = [];
     numberFields: string[] = [];
     booleanFields: string[] = [];
diff --git a/src/utils/dsv-parser.ts b/src/utils/dsv-parser.ts
index e66e831..0b6a2c1 100644
--- a/src/utils/dsv-parser.ts
+++ b/src/utils/dsv-parser.ts
@@ -12,10 +12,10 @@ export function parseCsv(content: string, options?: ParsingOptions): any[] {
     return getLineTokens(content, options || new ParsingOptions());
 }
 
-export function toCsv(array: any[], delimiter: string = ','): string {
+export function toCsv(array: any[], delimiter = ','): string {
     array = array || [];
 
-    var result = "";
+    const result = "";
     const headers: string[] = [];
 
     // workout all headers
@@ -47,8 +47,8 @@ export function toCsv(array: any[], delimiter: string = ','): string {
 }
 
 type ParsingContext = {
-    content: string,
-    currentIndex: number
+    content: string;
+    currentIndex: number;
 };
 
 function getObjectElement(fieldNames: string[], tokens: string[], options: ParsingOptions): any {
@@ -135,7 +135,7 @@ function getLineTokens(content: string, options: ParsingOptions): string[][] {
     return result;
 }
 
-function nextLineTokens(context: ParsingContext, delimiter: string = ','): string[] {
+function nextLineTokens(context: ParsingContext, delimiter = ','): string[] {
     const tokens: string[] = [];
     let token = '';
 
diff --git a/tsconfig.json b/tsconfig.json
index c6ed90a..92d9b71 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -44,7 +44,7 @@
     // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
     // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
     // "typeRoots": [],                       /* List of folders to include type definitions from. */
-    // "types": [],                           /* Type declaration files to be included in compilation. */
+    "types": ["node", "jest"],                           /* Type declaration files to be included in compilation. */
     // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
     "esModuleInterop": true,                  /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
     // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */