// Functions

// Helps in appying the `DRY` principle ,i.e., Don't Repeat Yourself.

// Function declaration

function calculateAge(birthYear) {

return 2019 - birthYear;

}

var ageSilver = calculateAge(1999);

console.log(ageSilver);

function yearsUntilRetirement(birthYear, firstName) {

var age = calculateAge(birthYear);

var retirement = (firstName === 'Silver' || firstName == 'silver') ? NaN : 65 - age;

if (retirement > 0) {

console.log(firstName + ' retires in ' + retirement + ' years.');

} else if (retirement || retirement === 0) {

console.log(firstName + ' is already retired.');

} else {

console.log(firstName + ' never retires.');

}

}

yearsUntilRetirement(1999, 'Silver');

yearsUntilRetirement(1998, 'Rohan');

yearsUntilRetirement(1953, 'Rahul');

yearsUntilRetirement(1954, 'Manish');

// ---------------------------------- Function Statements and Expressions ---------------------------------------------

// ----- Function declaration (statement) method -----

// function whatDoYouDo(job, firstName) { ... }

// ----- Function Expression method -----

var whatDoYouDo = function(job, firstName) {

switch(job) {

case 'teacher':

case 'instructor':

return firstName + ' teaches kids how to code.';

case 'driver':

return firstName + 'drives the taxi.';

case 'designer':

return firstName + 'designs the interactive webpages.';

default:

return firstName + ' do something else';

}

}

console.log(whatDoYouDo('designer', 'Silver'));

console.log(whatDoYouDo('teacher', 'Shiba'));

console.log(whatDoYouDo('cop', 'Celin'));

// There are two main fundamental concepts in JavaScript:

// - Expressions

// - Statements

// Expressions in JavaScript are pieces of code that always produce a value and it doesn't matter how long they are as

// long as they gives a single value. So, in JavaScript whenever we require a value we need to write an expression.

// Wheter statements are those piece of codes which do not give an immidiate result like - if/else, loops, function

// declaration, etc.