007-Undefined_Null_NaN_Empty.js

/* 
 * Author : Jaydatt Patel
Undefined, Null, Empty, NaN

Undefined : if variable or function does not have value then it returns undefined
Null : It is returned if value is not found.

NaN : Is is returned if arithmetic operation fail with undefined, null, string or else.

(0 , null, undefined, Nan) are false value also called falsy.
*/

//Undefined : if variable or function does not have value then it returns undefined
var val;
console.log("val : ", val);
//console.log(a); ReferenceError: a is not defined
var game = { score: 100 };
console.log("game.sc : ", game.sc);
//console.log(a); ReferenceError: a is not defined

//Null is returned if value is not found
var str = "ABC";
console.log('str.match("B"): ', str.match("B"));
console.log('str.match("D"): ', str.match("D"));

var result = null;
console.log("result : ", result);

//Empty
var set = ""; //string
var set2 = []; //array
var set3 = {}; //object
console.log(set);
console.log(set2);
console.log(set3);

//sample program
var x;

if (x === null) {
  console.log("x is null");
} else if (x === undefined) {
  console.log("x is undefined");
} else {
  console.log("x is ok");
}
console.log("--------------------");
//(0 , null, undefined, Nan) are false value also called falsy.
console.log("3 && 4 && 5 && 1 && 2 : ", 3 && 4 && 5 && 1 && 2);
console.log("3 && 4 && 5 && null && 1 && 2 : ", 3 && 4 && 5 && null && 1 && 2);
console.log(
  "3 && 4 && 5 && undefined && 1 && 2 : ",
  3 && 4 && 5 && undefined && 1 && 2
);
console.log("3 && 4 && 5 && NaN && 1 && 2 : ", 3 && 4 && 5 && NaN && 1 && 2);

console.log("--------------------");

console.log("0 && null && undefined && NaN : ", 0 && null && undefined && NaN);
console.log("null && undefined && NaN && 0 : ", null && undefined && NaN && 0);
console.log("undefined && NaN && 0 && null : ", undefined && NaN && 0 && null);
console.log("NaN && 0 && null && undefined : ", NaN && 0 && null && undefined);

console.log("--------------------");

console.log("0 || null || undefined || NaN :", 0 || null || undefined || NaN);
console.log(
  "0 || null || undefined || 123 || NaN :",
  0 || null || undefined || 123 || NaN
);
console.log(
  "0 || null || 'string' || undefined || NaN :",
  0 || null || "string" || undefined || NaN
);