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/********************************************************************************************
* Functions: Declarations, Statements & Expressions.
*/
// Function Declaration
function calculateAge (YOB) {
// YOB: Year of Birth
var currYear = 2019;
return currYear - YOB;
}
// Function Statement is calling the function after it was defined
var johnAge = calculateAge(1990);
var ramkiAge = calculateAge(1955);
var ramAge = calculateAge(1995);
console.log("John's Age: " + johnAge + "; " +
"Ramki's Age: " + ramkiAge + "; " +
"Ram's Age: " + ramAge + ";");
// Function Declaration that doesn't return anything
function yearsUntilRetirement (birthYear, firstName) {
var age = calculateAge(birthYear);
var retirement = 58 - age; // Retirement Age in India is 58
var retirementStatus = retirement < 0 ? "retired" : "not retired";
if (retirementStatus === "not retired")
console.log(firstName + " still has " + retirement + " years for retirement");
else console.log("It has been " + (-retirement) + " years since " + firstName + " has retired");
}
yearsUntilRetirement(johnAge, "John");
yearsUntilRetirement(ramkiAge, "Ramki");
yearsUntilRetirement(ramAge, "Ram");
// Function Declaration is as follows:
// function occupation(job, firstName) {}
// Same as the declarations as we have seen above.
// But, Function Expressions are anonymous functions that are assigned to a JS variable/object as follows:
var occupation = function (job, firstName) {
var doesThis = "";
switch(job) {
case "teacher":
doesThis += "is a teacher who teaches how to code";
break;
case "driver":
doesThis += "is a truck driver";
break;
case "coder":
case "software engineer":
doesThis += "is a software engineer working at xyz company";
break;
case "designer":
doesThis += "is a system designer working for xyz company";
break;
default:
doesThis += "does something else";
}
return firstName + " " + doesThis;
}
var johnJob = "teacher", ramkiJob = "retired", ramJob = "coder";
console.log(occupation(johnJob, "John"));
console.log(occupation(ramkiJob, "Ramki"));
console.log(occupation(ramJob, "Ram"));
/********************************************************************************************
* Expressions vs. Statements in JS
* --------------------------------
*
* In JS, Expressions return something explicit immediately, whereas statements do not return
* something immediately. The above anonymous function is assigned to occupation
* variable, it means that whenever we call occupation, we basically are expecting something
* in return. But whenever a statement like if(), while(), for(), etc are used, they'll
* obviously do something with the code, but they themselves never return anything explicit.
*
*
* statement example:
* > if(true) {console.log(45);}
* This is a statement. if() will return undefined. But since console.log(45) is an
* expression, we will get a return value of 23. If we copy and paste this line in
* the browser, we will get undefined & 45 as the return value.
*
* expression example:
* > occupation(johnJob, "John");
* This line here is an expression and definitely returns something. If we open the
* HTML page related to this JS page in the browser & open the console and copy-paste
* the line of code above, we will see that it returns some kind of a value, which
* is not undefined.
*/