Comparison between JavaScript's "null" and "undefined" keywords [duplicate]

I felt that I just contribute to content on the JavaScript's null and undefined keywords, which I feel might be helpful to especially some new JavaScript programmers that seek to understand these keywords. Below I took time to compare these two, using some if-statements to do some things if conditions translated to true, and do otherwise, something else if translated to false. NB: When a variable is just declared without being assigned any value, JavaScript assigns undefined to that variable, where as null is usually always assigned by a programmer; I prove the first part of this note, hereinbefore, in the last console.log()-statement which translates to the Boolean value, true.

let firstValue = null,
  secondValue; // Declared without value assignment.

if (firstValue === secondValue) {
  console.log('"null" is explicitly equal to "undefined".');
} else {
  console.log('"null" is NOT explicitly equal to "undefined".');
}

if (firstValue == secondValue) {
  console.log('"null" is somewhat equal to "undefined".');
} else {
  console.log('"null" is NOT equal to "undefined" at all!');
}

if (firstValue) {
  console.log('"null" is truthy.');
} else {
  console.log('"null" is falsey.');
}

if (secondValue) {
  console.log('"undefined" is truthy.');
} else {
  console.log('"undefined" goes to falsey.');
}

console.log(undefined === secondValue);

Below is the result of the above code:

"null" is NOT explicitly equal to "undefined".   main.js:11 
"null" is somewhat equal to "undefined".         main.js:19 
"null" is falsey.                                main.js:25 
"undefined" goes to falsey.                      main.js:28 
true //Boolean Value.

FACT: Both values translate to false, but are not explicitly equal to each other.