some corrections

Author: Asabeneh

02_Day_Data_types/02_day_data_types.md

@@ -231,6 +231,10 @@ console.log(Math.E)             // 2.718
 console.log(Math.log(2))        // 0.6931471805599453
 console.log(Math.log(10))       // 2.302585092994046
 
+// Returns the natural logarithm of 2 and 10 respectively
+console.log(Math.LN2)           // 0.6931471805599453
+console.log(Math.LN10)          // 2.302585092994046
+
 // Trigonometry
 Math.sin(0)
 Math.sin(60)

02_Day_Data_types/string_methods/match.js

@@ -14,7 +14,7 @@ let pattern = /love/gi
 console.log(string.match(pattern)) // ["love", "love", "love"]
 // Let us extract numbers from text using regular expression. This is not regular expression section, no panic.
 
-let txt = 'In 2019, I run 30 Days of Pyhton. Now, in 2020 I super exited to start this challenge'
+let txt = 'In 2019, I run 30 Days of Python. Now, in 2020 I super exited to start this challenge'
 let regEx = /\d/g // d with escape character means d not a normal d instead acts a digit
 // + means one or more digit numbers, 
 // if there is g after that it means global, search everywhere.

02_Day_Data_types/string_methods/split.js

@@ -1,5 +1,5 @@
 // split(): The split method splits a string at a specified place.
-let string = '30 Days Of JavaScipt'
+let string = '30 Days Of JavaScript'
 console.log(string.split())     // ["30 Days Of JavaScript"]
 console.log(string.split(' '))  // ["30", "Days", "Of", "JavaScript"]
 let firstName = 'Asabeneh'

03_Day_Booleans_operators_date/03_booleans_operators_date.md

@@ -31,7 +31,7 @@
 		- [Increment Operator](#increment-operator)
 		- [Decrement Operator](#decrement-operator)
 		- [Ternary Operators](#ternary-operators)
-		- [Operator Precendence](#operator-precendence)
+		- [Operator Precedence](#operator-precedence)
 	- [Window Methods](#window-methods)
 		- [Window alert() method](#window-alert-method)
 		- [Window prompt() method](#window-prompt-method)
@@ -333,9 +333,9 @@ number > 0
 -5 is a negative number
 ```
 
-### Operator Precendence
+### Operator Precedence
 
-I would like to recommend you to read about operator precendence from this [link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence)
+I would like to recommend you to read about operator precedence from this [link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence)
 
 ## Window Methods
 
@@ -568,9 +568,9 @@ console.log(`${date}/${month}/${year} ${hours}:${minutes}`) // 4/1/2020 0:56
 1. Get length and width using prompt and calculate an area of rectangle (area = length x width and the perimeter of rectangle (perimeter = 2 x (length + width))
 1. Get radius using prompt and calculate the area of a circle (area = pi x r x r) and circumference of a circle(c = 2 x pi x r) where pi = 3.14.
 1. Calculate the slope, x-intercept and y-intercept of y = 2x -2
-1. Slope is (m = y2-y1/x2-x1). Find the slope between point (2, 2) and point(6,10)
+1. Slope is m = (y<sub>2</sub>-y<sub>1</sub>)/(x<sub>2</sub>-x<sub>1</sub>). Find the slope between point (2, 2) and point(6,10)
 1. Compare the slope of above two questions.
-1. Calculate the value of y (y = x^2 + 6x + 9). Try to use different x values and figure out at what x value y is 0.
+1. Calculate the value of y (y = x<sup>2</sup> + 6x + 9). Try to use different x values and figure out at what x value y is 0.
 1. Writ a script that prompt a user to enter hours and rate per hour. Calculate pay of the person?
 
     ```sh

04_Day_Conditionals/04_day_conditionals.md

@@ -280,7 +280,7 @@ isRaining
 
 ### Exercises: Level 1
 
-1. Get user input using prompt(“Enter your age:”). If user is 18 or older , give feedback:'You are old enough to drive' but if not 18 give another feedback stating to  wait for the number of years he neds to turn 18.
+1. Get user input using prompt(“Enter your age:”). If user is 18 or older , give feedback:'You are old enough to drive' but if not 18 give another feedback stating to  wait for the number of years he needs to turn 18.
 
    ```sh
    Enter your age: 30

05_Day_Arrays/05_day_arrays.md

@@ -18,35 +18,35 @@
 ![Day 5](../images/banners/day_1_5.png)
 
 - [📔 Day 5](#-day-5)
-  - [Arrays](#arrays)
-    - [How to create an empty array](#how-to-create-an-empty-array)
-    - [How to create an array with values](#how-to-create-an-array-with-values)
-    - [Creating an array using split](#creating-an-array-using-split)
-    - [Accessing array items using index](#accessing-array-items-using-index)
-    - [Modifying array element](#modifying-array-element)
-    - [Methods to manipulate array](#methods-to-manipulate-array)
-      - [Array Constructor](#array-constructor)
-      - [Creating static values with fill](#creating-static-values-with-fill)
-      - [Concatenating array using concat](#concatenating-array-using-concat)
-      - [Getting array length](#getting-array-length)
-      - [Getting index an element in arr array](#getting-index-an-element-in-arr-array)
-      - [Getting last index of an element in array](#getting-last-index-of-an-element-in-array)
-      - [Checking array](#checking-array)
-      - [Converting array to string](#converting-array-to-string)
-      - [Joining array elements](#joining-array-elements)
-      - [Slice array elements](#slice-array-elements)
-      - [Splice method in array](#splice-method-in-array)
-      - [Adding item to an array using push](#adding-item-to-an-array-using-push)
-      - [Removing the end element using pop](#removing-the-end-element-using-pop)
-      - [Removing an element from the beginning](#removing-an-element-from-the-beginning)
-      - [Add an element from the beginning](#add-an-element-from-the-beginning)
-      - [Reversing array order](#reversing-array-order)
-      - [Sorting elements in array](#sorting-elements-in-array)
-    - [Array of arrays](#array-of-arrays)
-  - [💻 Exercise](#-exercise)
-    - [Exercise: Level 1](#exercise-level-1)
-    - [Exercise: Level 2](#exercise-level-2)
-    - [Exercise: Level 3](#exercise-level-3)
+	- [Arrays](#arrays)
+		- [How to create an empty array](#how-to-create-an-empty-array)
+		- [How to create an array with values](#how-to-create-an-array-with-values)
+		- [Creating an array using split](#creating-an-array-using-split)
+		- [Accessing array items using index](#accessing-array-items-using-index)
+		- [Modifying array element](#modifying-array-element)
+		- [Methods to manipulate array](#methods-to-manipulate-array)
+			- [Array Constructor](#array-constructor)
+			- [Creating static values with fill](#creating-static-values-with-fill)
+			- [Concatenating array using concat](#concatenating-array-using-concat)
+			- [Getting array length](#getting-array-length)
+			- [Getting index an element in arr array](#getting-index-an-element-in-arr-array)
+			- [Getting last index of an element in array](#getting-last-index-of-an-element-in-array)
+			- [Checking array](#checking-array)
+			- [Converting array to string](#converting-array-to-string)
+			- [Joining array elements](#joining-array-elements)
+			- [Slice array elements](#slice-array-elements)
+			- [Splice method in array](#splice-method-in-array)
+			- [Adding item to an array using push](#adding-item-to-an-array-using-push)
+			- [Removing the end element using pop](#removing-the-end-element-using-pop)
+			- [Removing an element from the beginning](#removing-an-element-from-the-beginning)
+			- [Add an element from the beginning](#add-an-element-from-the-beginning)
+			- [Reversing array order](#reversing-array-order)
+			- [Sorting elements in array](#sorting-elements-in-array)
+		- [Array of arrays](#array-of-arrays)
+	- [💻 Exercise](#-exercise)
+		- [Exercise: Level 1](#exercise-level-1)
+		- [Exercise: Level 2](#exercise-level-2)
+		- [Exercise: Level 3](#exercise-level-3)
 
 # 📔 Day 5
 
@@ -390,22 +390,22 @@ Check an element if it exist in an array.
 const fruits = ['banana', 'orange', 'mango', 'lemon']
 let index = fruits.indexOf('banana')  // 0
 
-if(index != -1){
-   console.log('This fruit does exist in the array')  
+if(index === -1){
+   console.log('This fruit does not exist in the array')  
 } else {
-    console.log('This fruit does not exist in the array')
+    console.log('This fruit does exist in the array')
 }
 // This fruit does exist in the array
 
 // we can use also ternary here
-index != -1 ? console.log('This fruit does exist in the array'): console.log('This fruit does not exist in the array')
+index === -1 ? console.log('This fruit does not exist in the array'): console.log('This fruit does exist in the array')
 
 // let us check if a avocado exist in the array
 let indexOfAvocado = fruits.indexOf('avocado')  // -1, if the element not found index is -1
-if(indexOfAvocado!= -1){
-   console.log('This fruit does exist in the array')  
+if(indexOfAvocado === -1){
+   console.log('This fruit does not exist in the array')  
 } else {
-    console.log('This fruit does not exist in the array')
+    console.log('This fruit does exist in the array')
 }
 // This fruit does not exist in the array
 ```

06_Day_Loops/06_day_loops.md

@@ -18,17 +18,17 @@
 ![Day 5](../images/banners/day_1_6.png)
 
 - [📔 Day 6](#-day-6)
-  - [Loops](#loops)
-    - [for Loop](#for-loop)
-    - [while loop](#while-loop)
-    - [do while loop](#do-while-loop)
-    - [for of loop](#for-of-loop)
-    - [break](#break)
-    - [continue](#continue)
-  - [💻 Exercises:Day 6](#-exercisesday-6)
-    - [Exercises: Level 1](#exercises-level-1)
-    - [Exercises: Level 2](#exercises-level-2)
-    - [Exercises: Level 3](#exercises-level-3)
+	- [Loops](#loops)
+		- [for Loop](#for-loop)
+		- [while loop](#while-loop)
+		- [do while loop](#do-while-loop)
+		- [for of loop](#for-of-loop)
+		- [break](#break)
+		- [continue](#continue)
+	- [💻 Exercises:Day 6](#-exercisesday-6)
+		- [Exercises: Level 1](#exercises-level-1)
+		- [Exercises: Level 2](#exercises-level-2)
+		- [Exercises: Level 3](#exercises-level-3)
 
 # 📔 Day 6
 
@@ -178,7 +178,9 @@ for (const num of numbers) {
 // adding all the numbers in the array
 let sum = 0
 for (const num of numbers) {
-  sum = sum + num  // can be also shorten like this, sum += num
+  sum = sum + num  
+	// can be also shorten like this, sum += num
+  // after this we will use the shorter synthax(+=, -=, *=, /= etc)
 }
 console.log(sum) // 15
 

07_Day_Functions/07_day_functions.md

@@ -239,7 +239,7 @@ function sumAllNums() {
   console.log(arguments)
 }
 
-sumAllNums(1, 2, 3, 4)) 
+sumAllNums(1, 2, 3, 4)
 // Arguments(4) [1, 2, 3, 4, callee: ƒ, Symbol(Symbol.iterator): ƒ]
 
 ```
@@ -269,7 +269,7 @@ console.log(sumAllNums(15, 20, 30, 25, 10, 33, 40))  // 173
 ​
 const sumAllNums = (...args) => {
   // console.log(arguments), arguments object not found in arrow function
-  // instead we use an a parameter followed by spread operator
+  // instead we use a parameter followed by spread operator (...)
   console.log(args)
 }
 
@@ -523,7 +523,7 @@ It Will be covered in other section.
 9. Density of a substance is calculated as follows:_density= mass/volume_. Write a function which calculates _density_.
 10. Speed is calculated by dividing the total distance covered by a moving object divided by the total amount of time taken. Write a function which calculates a speed of a moving object, _speed_.
 11. Weight of a substance is calculated as follows: _weight = mass x gravity_. Write a function which calculates _weight_.
-12. Temperature in oC can be converted to oF using this formula: _oF = (oC x 9/5) + 32_. Write a function which convert oC to oF _convertCelciusToFahrenheit_.
+12. Temperature in oC can be converted to oF using this formula: _oF = (oC x 9/5) + 32_. Write a function which convert oC to oF _convertCelsiusToFahrenheit_.
 13. Body mass index(BMI) is calculated as follows: _bmi = weight in Kg / (height x height) in m2_. Write a function which calculates _bmi_. BMI is used to broadly define different weight groups in adults 20 years old or older.Check if a person is _underweight, normal, overweight_ or _obese_ based the information given below.
 
     - The same groups apply to both men and women.

08_Day_Objects/08_day_objects.md

@@ -18,50 +18,49 @@
 ![Thirty Days Of JavaScript](../images/banners/day_1_8.png)
 
 - [📔 Day 8](#-day-8)
-  - [Scope](#scope)
-    - [Window Scope](#window-scope)
-    - [Global scope](#global-scope)
-    - [Local scope](#local-scope)
-  - [📔 Object](#-object)
-    - [Creating an empty object](#creating-an-empty-object)
-    - [Creating an objecting with values](#creating-an-objecting-with-values)
-    - [Getting values from an object](#getting-values-from-an-object)
-    - [Creating object methods](#creating-object-methods)
-    - [Setting new key for an object](#setting-new-key-for-an-object)
-    - [Object Methods](#object-methods)
-      - [Getting object keys using Object.keys()](#getting-object-keys-using-objectkeys)
-      - [Getting object values using Object.values()](#getting-object-values-using-objectvalues)
-      - [Getting object keys and values using Object.entries()](#getting-object-keys-and-values-using-objectentries)
-      - [Checking properties using hasOwnProperty()](#checking-properties-using-hasownproperty)
-  - [💻 Exercises](#-exercises)
-    - [Exercises: Level 1](#exercises-level-1)
-    - [Exercises: Level 2](#exercises-level-2)
-    - [Exercises: Level 3](#exercises-level-3)
+	- [Scope](#scope)
+		- [Window Global Object](#window-global-object)
+		- [Global scope](#global-scope)
+		- [Local scope](#local-scope)
+	- [📔 Object](#-object)
+		- [Creating an empty object](#creating-an-empty-object)
+		- [Creating an objecting with values](#creating-an-objecting-with-values)
+		- [Getting values from an object](#getting-values-from-an-object)
+		- [Creating object methods](#creating-object-methods)
+		- [Setting new key for an object](#setting-new-key-for-an-object)
+		- [Object Methods](#object-methods)
+			- [Getting object keys using Object.keys()](#getting-object-keys-using-objectkeys)
+			- [Getting object values using Object.values()](#getting-object-values-using-objectvalues)
+			- [Getting object keys and values using Object.entries()](#getting-object-keys-and-values-using-objectentries)
+			- [Checking properties using hasOwnProperty()](#checking-properties-using-hasownproperty)
+	- [💻 Exercises](#-exercises)
+		- [Exercises: Level 1](#exercises-level-1)
+		- [Exercises: Level 2](#exercises-level-2)
+		- [Exercises: Level 3](#exercises-level-3)
 
 # 📔 Day 8
 
 ## Scope
 
-Variable is the fundamental part in programming. We declare variable to store different data types. To declare a variable we use the key word _var_, _let_ and _const_. A variable can declared at different scope. In this section we will see the scope, scope of variables when we use var or let.
+Variable is the fundamental part in programming. We declare variable to store different data types. To declare a variable we use the key word _var_, _let_ and _const_. A variable can be declared at different scope. In this section, we will see the scope variables, scope of variables when we use var or let.
 Variables scopes can be:
 
-- Window
 - Global
 - Local
 
-Variable can be declared globally or locally or window scope. We will see both global and local scope.
-Anything declared without let, var or const is scoped at window level.
+Variable can be declared globally or locally  scope. We will see both global and local scope.
+Anything declared without let, var or const is scoped at global level.
 
 Let us imagine that we have a scope.js file.
 
-### Window Scope
+### Window Global Object
 
 Without using console.log() open your browser and check, you will see the value of a and b if you write a or b on the browser. That means a and b are already available in the window.
 
 ```js
 //scope.js
-a = 'JavaScript' // is a window scope this found anywhere
-b = 10 // this is a window scope variable
+a = 'JavaScript' // declaring a variable without let or const make it available in window object and this found anywhere
+b = 10 // this is a global scope variable and found in the window object
 function letsLearnScope() {
   console.log(a, b)
   if (true) {
@@ -96,13 +95,18 @@ console.log(a, b) // JavaScript 10, accessible
 
 A variable declared as local can be accessed only in certain block code.
 
+- Block Scope
+- Function Scope
+
 ```js
 //scope.js
 let a = 'JavaScript' // is a global scope it will be found anywhere in this file
 let b = 10 // is a global scope it will be found anywhere in this file
+// Function scope
 function letsLearnScope() {
   console.log(a, b) // JavaScript 10, accessible
   let value = false
+// block scope
   if (true) {
     // we can access from the function and outside the function but 
     // variables declared inside the if will not be accessed outside the if block
@@ -111,7 +115,7 @@ function letsLearnScope() {
     let c = 30
     let d = 40
     value = !value
-    console.log(a, b, c) // Python 20 30
+    console.log(a, b, c, value) // Python 20 30 true
   }
   // we can not access c because c's scope is only the if block
   console.log(a, b, value) // JavaScript 10 true
@@ -138,9 +142,9 @@ if (true){
 console.log(gravity)  // 9.81
 
 for(var i = 0; i < 3; i++){
-  console.log(i) // 1, 2, 3
+  console.log(i) // 0, 1, 2
 }
-console.log(i)
+console.log(i) // 3
 
 ```
 
@@ -163,13 +167,13 @@ if (true){
 // console.log(gravity), Uncaught ReferenceError: gravity is not defined
 
 for(let i = 0; i < 3; i++){
-  console.log(i) // 1, 2, 3
+  console.log(i) // 0, 1, 2
 }
 // console.log(i), Uncaught ReferenceError: i is not defined
 
 ```
 
-The scope *let* and *const* is the same. The difference is only reassigning. We can not change or reassign the value of const variable. I would strongly suggest you to use *let* and *const*, by using *let* and *const* you will writ clean code and avoid hard to debug mistakes. As a rule of thumb, you can use *let* for any value which change, *const* for any constant value, and for array, object, arrow function and function expression.
+The scope *let* and *const* are the same. The difference is only reassigning. We can not change or reassign the value of the `const` variable. I would strongly suggest you to use *let* and *const*, by using *let* and *const* you will write clean code and avoid hard to debug mistakes. As a rule of thumb, you can use *let* for any value which change, *const* for any constant value, and for an array, object, arrow function and function expression.
 
 ## 📔 Object
 
@@ -252,14 +256,14 @@ const person = {
 console.log(person.firstName)
 console.log(person.lastName)
 console.log(person.age)
-console.log(person.location)
+console.log(person.location) // undefined
 
 // value can be accessed using square bracket and key name
 console.log(person['firstName'])
 console.log(person['lastName'])
 console.log(person['age'])
 console.log(person['age'])
-console.log(person['location'])
+console.log(person['location']) // undefined
 
 // for instance to access the phone number we only use the square bracket method
 console.log(person['phone number'])