True False values ,Logical Operators and Short-circuit Evaluation in Javascript

 1.Truthy and Falsy values :

In javascript, any variable with a value, such as a string that has characters in it,

a numeric that is non-zero,or a Boolean true is considered true,and you can use it in an 

if statement like that.

Any variable that is a Boolean false,null,undefined,Not a number,or an empty string is considered false.

ex : check for 'truth' values 

     let price =100;

let color = "Red";

 

   // Check if price has something other than zero  

   

if(price){

   console.log("Price is > 0");        // Price is > 0

}

 

 

   // Check if color has characters in it.

   

     if(color){

  console.log("color has a value");    // color has a value

}   

  ex: check for 'false' values 

  

    let color = "Red";

  // Set value to null, it becomes false

    color =null;

    console.log("color == null = " + Boolean(color)); // color == null = false

 

  // Set value to empty string, it becomes false

    color ="";

console.log("color == '' = " + Boolean(color));     // color == '' = false

  // Set value to undefined,it becomes false

   color=undefined;

   console.log(" color == undefined = " + Boolean(color));  // color == undefined = false

   

 // Declare variable and don't initialize, it is false

   let value;

   console.log(" ' let value ' = " + Boolean(value));       // ' let value ' = false

   

  // Result of NaN is false

  value = 100/"test";

  console.log(" 100 / 'test' = " + Boolean(value));        // 100 / 'test' = false

  

2.Logical Operators

Logical AND (&&):

In javascript, the logical AND operator will return true if both operands are true.

When using the AND operator, both sides must return true for the expression to be true.

Logical OR (||):

In javascript, the logical OR operator returns true if either operand is true.

When using the OR opeartor,only one expression needs to be true for the expression to be true;

Logical NOT (!) :

In javascript, the logical NOT operator negate anything

3.short Circuiting :

-> short circuiting is simply an optimization for logical expressions.

-> short circuiting allows javascript to do is to bypass subsequent expressions in And or Or conditions based on truthy or falsy.

ex : short circuiting (&&)

    let result;

// if first result is false, the second part is never evaluated

result = isColorRed("Black") && isGreaterThan1400(1400);  // false

function isColorRed(value){

console.log("In the isColorRed() function");

return value === "Red";

}

    

function isGreaterThan1400(value){

console.log(" In the isGreaterThan1400() function");

return value > 1400;

}

 

  ex : short circuiting (||)

       

   let result;

   

   // Each expression is evaluated until one returns a true

   

   result= isColorRed("Red") || isGreaterThan1400(200);  // true

   

   // In the isColorRed() function

   

   // Each expression is evaluated until one returns a true the rest are then skipped

   

   result = isGreaterThan1400(200) || isColorRed("Black");  // false

   

   // In the isGreaterThan1400() function

       // In the isColorRed() function