This is a repository that contains my notes about javascript, as a Java Developer I omitted many part of the javascript fundamentals for similarities reasons between java and Js.

To learn more about Javascript from wikipedia, visit the following link.

• In Javascript, we don't declare the type of the data, for example we can declare and initialize a number variable like that var n=1, later in the program we can also change the type of the variable n="nowitisastringvariable". In java for example we need to declare it as follows: int n=1, later in the program we can't change the type of n.
• Javascript is a dynamically typed language, to learn more, check the following links: 1, 2.

There are two categories of javascript data, the primitive data types and the complex data types.

• number: one type for decimals and floats, var n=3.14.

• string: "str1", 'str2', `str3`

• boolean: true or false

• undefined: When we create a variable without assigning a value to it, its value will be undefined, its type also will be undefined.

• null: means an empty value, var n=null, the value of n will be null and the type of n will be object.

• Primitives types are passed by value:

  

There are two types in this category, arrays and objects.

• array: [1,'str1',true], arrays are 0 indexed, they can contains heterogenous types, objects type included: [1,'str1',true, {key1: 1.5}] .

• object: {key1:"value1", key2: 1.5, key3: true}

• Complex types are passed by reference:

  

• Returned anytime a method expect a number input, and the caller pass a non number, the following expression will return NaN: Math.sqrt('Mehdi the special one')
• typeof NaN will return number.
• To check if a given value is of type NaN, we can use the function isNaN(Math.sqrt('Mehdi the special one)).
• keep in mind that console.log(NaN == NaN) will result to false.

• 45 == 45 will return true, we check if the two are equal.
• 45 === "45" will return false, we check if both are equal and their type is the same, it is called the strict equal.
• 5 != "5" will return false, we check if the two numbers are not equal.
• 5 !== "5" will return true, we check if the two numbers are not equal or they don't have the same type.

• function declaration:

      function functionName(param1, param2){
          //body of the function
          // the possibility to return a value
          //the returned value can be of any type, even a function
      }
  

• a return keyword without an expression after it, will cause the function to return undefined, the samething happens when we don't have a return statement.
• If we pass too many parameters to a function, the extra ones are ignored, if we pass too few, the missing parameters get assigned undefined as a value.

• JavaScript is a weakly dynamic language, to read more about that, check the following links: 1, 2, 3.

• String(10) will return a string data type.
• Number("1") will return a number data type.
• Boolean("string")

• performed by javascript behind the scene, "5"/2 will return 2.5.

• Global scope, local scope, block scope, function hoising, function scope, nested scopes

• Using the var keyword, we can create two variables with the same name

  

• As we can see in the above example, the variable one is a global variable and can be accessed from anywhere, the number variable declared with let keyword is local to its function and can not be accessed globally, the variable three even with the var keyword can not be accessed globally because its scope is the same as the function innerFunction() and can only be accessed inside the getApi function. For more details about scopes, visit the following links, 1, 2.

• For those reasons, it is recommended to use the let or the const keywords whenever possible.

• A closure gives you access to an outer function's scope from an inner function, for more details check 1, 2.
• More on closure, here.

• Article about this keyword: 1, 2, 3.

• If a variable is declared inside a function, this variable can not be accessed outside the function. We say the variable has a function scope. In case, it is declared inside a block, we say that is block scoped variable and it can be accessed outside of the scope

  

• We can't declare two variable with the same name inside the same scope, the variable declared with let is said to be block scoped, an example to make it more clear. let

• Map this keyword without using the bind method.

• Shorter and concise code.

• Code hard to read.

• Two ways to write arrow functions

  

• Example on template literals

• arrays
• objects
• functions

• Examples

  

• Examples

• Examples

• Articles about Promise: medium,mozilla,about Promise race,4, promise-api.
• Examples
• async and await
• async and await:

• Semicolon in Js.
• Expression Vs Statement: 1, 2, 3.
• Is javascript an interpreted or compiled language: 1, 2, 3.
• Function hoising 1, 2, 3.