foundation 1 and 2 notes

Author: INDRESH-009

js_notes/foundation1.js

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+/* Foundations of js - 01 -> PRIME FOCUS = basics of variables and datatypes*/
+
+/*
+1.What are value 
+2.What is a variable 
+3.what are datatypes
+4.what are 7 primitive datatypes
+5.3 ways to Declare a variable in js - let,const,var
+6.console.log function
+7.Type of operator 
+8.Whats Dynamic typing & its action
+9.Comments in JS
+*/
+
+// 1. What are values - its a piece of data - 13 , 12.89 , true , 'Indresh' etc
+
+// 2. What is a variable - All tasks in software deals with data and thus it is essential to store it. Variables are containers that can store values/data
+
+// 3. What is a datatype - values can be of different types.  These are called datatypes. In JS values are of broadly 2 types -> primitive datatypes and objects
+
+// 4. what are 7 primitive datatypes
+/*
+    -> Numbers = both int and floats 
+    -> String = Sequence of characters in quotes
+    -> Boolean = logical datatype whose values are - true or false 
+    -> undefined = means empty value & If a variable is declared and not yet initialised it takes up this datatype as default 
+    -> null = indicates empty/no value and is a assigned value intentionally
+    -> Bigint = ES2020 feature - stores large numbers 
+    -> Symbol = ES2015 feature - represents values that are unique and cant be changed 
+    */
+
+// 5. Declaring and initialising a variable
+/* declaring Syntax-> keyword variablename ;
+       initialising Synatx -> variablename = value;
+
+       There are 3 keywords to declare a variable 
+       1.let keyword -> used to declare those variables whose values may be mutated in future
+       2.const keyword -> used to declare those variables whose values are not going to be changed/reassigned/mutated
+       3.var keyword -> shd be completely avoided after ES6  
+    */
+       let num1; //declaring
+       num1 = 10; //initialising
+       let num2 = 12; //declaring and initialing at the same time
+       num1 = 15; //reassigning/mutating/changing the value of variable num1
+       
+       const fullname = "Indresh"; //declaring and initialising shd be done at the same time for const keyword
+       //const class;               This gives error becz const variables cant be left without initialising
+       //Its preffered to keep most of your code in const if you are sure its not going to be mutated
+       
+       var a;
+       a = 10;
+       var b = 12;
+       //by this we see var is similar to let but there are some differences ->
+       /*Variables declared by let are only available inside the block where they're defined. Variables declared by var are available throughout the function in which they're declared*/
+       
+       // 6. console.log function
+       /*
+           -> It is a built-in function in js which when called prints/logs the contents in the console of the browser
+           */
+       console.log("Welcome javascript"); //logging a string
+       console.log(num1); //logging a variable
+       console.log(12); //logging a number
+       console.log(15 + 6); //logging an expression
+       console.log("hello " + fullname); //logging a concatenated string and variable
+       
+       // 7. Typeof operator
+       
+       //It tells us the datatype of a value/variable
+       console.log(typeof num1);
+       console.log(typeof fullname);
+       console.log(typeof true);
+       let x;
+       console.log(typeof x); // uninitialised variable - undefined datatype
+       let y = null;
+       console.log(typeof y); // gives output as object which is a bug and not resolved for legacy reason
+       
+       // 8. Dynamic typing in javascript
+       /* 
+       This means we dont havre to manually define the datatype of the value which the variable can store.
+        a variable can have any value belonging to any datatype
+        */
+       let dynamic = 10; //dynamic holds a num
+       dynamic = true; //dynamic holds a boolean
+       dynamic = "hello JS"; //dynamic holds a string
+       
+       // 9. Comments in JS
+       
+       /* multiline comment */
+       // single line comment

js_notes/foundation2.js

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+/* Foundations of js - 02 -> PRIME FOCUS = everything needed for Logical statements */
+
+/*
+1.What are statements and expressions
+2.What is a operator and a operand  -> operator precendence
+3.Concatenation of string by + operator & template literals
+4.Multiline strings before ES6 and after ES6 
+5.Conditional if-else statement
+6.Type conversion and type coercion in numbers , strings and boolean
+7.Equality operators (== vs ===)
+8.Inequality operators (!= vs !==)
+9.Switch statements in JS
+10.Conditional / terenary operator
+*/
+
+// 1. What is statements and expression
+/*
+Expression is a piece of code that is a value or produces/outputs a value
+3+4 , 15 , true && false , 23 > 13 , "hello" -> all these are values or gives a value after solving
+
+Statements is a piece of code that gives instructions and is executed but it doesnt hold any value of its own
+Many expressions combine to form a statement and they end with ;
+*/
+
+if (23 > 13) {
+    // this is a statement as whole, 23>13 is expression having a value of true
+    console.log("23 is greater than 13"); // this is a statement & the value inside console.log is an expression
+  }
+  
+  //The main reason to understad statemnenst and expressions is because JS expects an expression at a place where a value is expected and statements at a place where a value is not expected.
+  
+  //2. What is operator and operand
+  
+  //let us take an expression ->
+  2 + 5; //2,5 -> operand , + -> operator , 7 is the value of expression
+  true && false; //true,false -> operand , && -> operator , false is the value of expression
+  "hello" + "world"; //"hello" , "world" -> operand , + -> operator , "helloworld" is the value of expression
+  

js_notes/note.txt

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+js