JavaScript/ Function Basic

// ch20 Function 

function calcilateAge(birthYear){// you can also pass several var here
	return 2018-birthYear;
}

var ageJohn=calcilateAge(1990);// you just CALL function
var ageMike=calcilateAge(1948);
var ageJane=calcilateAge(1989);
console.log(ageJohn, ageMike, ageJane);// console printed // 28


function yearsUntilRetirement(year, firstName){
	var age = calcilateAge(year);
	var retire = 65 - age;
	if(retire>0){
	console.log(firstName+" retires in "+ retire+" years." );
}else{
	console.log(firstName+ " is already retired.");
}
}

yearsUntilRetirement(1990, "John"); // console printed // John retires in 37 years.
yearsUntilRetirement(1948, "Mike"); //Mike is already retired.
yearsUntilRetirement(1989, "Jane");

// ch21 Function Statements and Expressions

- function declairation
ex) function whatDoYouDo(job,firstName){}

- function expression
ex)

2+3, typeof...
-> they bring out immediate results.

var whatDoYouDo = function (job, firstName){
	switch (job){
		case "teacher":
			return firstName +" teaches kids how to code.";
		case "driver":
			return firstName +" drives a taxi.";
		case "designer":
			return firstName +" designs amazing clothes.";
		default:
			return firstName+" does nothing."
	}
}

console.log(whatDoYouDo("teacher", "John"));
console.log(whatDoYouDo("designer", "Jane"));
console.log(whatDoYouDo("none", "Jakob"));

- function statements: they don't bring out the result immediately.