There are 6 basic types in JS

• Numbers
• Strings
• Booleans
• Undefined
• Null
• Objects

typeof Operator

console.log(typeof "Hello World");
// String

console.log(typeof 9.9999);
// Number

console.log(typeof {name: "Adam", age: 23});
// Object

When an operator is applied to a wrong type of value, Javascript quietly converts it to appropriate type it needs using a set of predefined rules.

console.log("100" + 1);
// 1001

console.log("100" * 1);
// NaN

Standard de facto operators found in most of the programming languages

• Arithmetic ( - + / * % )

• Logical ( && || ! )

• Comparison ( > < == != === !== >= <= )

This concept can be used as a fallback mechanism for default values.

console.log("Adam" || "Eve");
// Adam
console.log(0 || 1);
// 1
console.log("Adam" && "Eve");
// Eve
console.log(0 && 1);
// 0

|| returns the value which is true and comes first.

&& returns the value which is false and comes first.

true || X - Here X is never evaluated. Once the left hand side of the || operator is true, it returns true.

Similarly, false && X - will return false without evaluating X

Any partial code fragment that returns a value is an Expression.

A Statement is a declaration that stands on its own and can affect the state of a machine.

The collection of bindings and statements at a given time is known as an Environment.

Bindings are like tentacles of an octopus, they just hold onto some values not contain them. Two bindings can refer to the same value.

let a = "Something";
console.log(a);
// Something

var b;
console.log(b);
// undefined

const PI = 3.14159
console.log(pi);
// 3.14159

PI = 3.9999 
// TypeError : Reassigning a const binding is not allowed

Control flow can be changed using any of the following :-

• Conditional Execution
  • if-else
  • switch-case
• Loops
  • while loop
  • do-while loop
  • for loop

// Single Line Comments

/*  This
    is 
    a
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*/