Mathew Kleppin
JavaScript Anyone?
Lesson 3
Conditions and Functions
What Makes a program
Programs made up of different things
Variables
Statements
Conditionals
Loops
Functions
Classes
First...
console.log
If you want to log something to the console while your program runs, we can use console.log to do it!
var name = "Matt";
console.log(name);
console.log(10 > 9);
console.log("Hello");
console.log("Hello".length);Conditionals
width = 154;
if(width >= 200){
//do something
}else if(width >= 100){
//do something
}else{
//fallback
}A conditonal statement checks something, and then executes something based on the check.
Conditionals
Make a program which displays a different message depending on an age. Here are the possible responses:
- age is less than 16, say "You can't drive."
- age is less than 18, say "You can't vote."
- age is less than 25, say "You can't rent a car."
- age is 25 or over, say "You can do anything!"
Conditionals
var age = 22;
if(age < 16){
console.log('You can\'t drive');
}else if(age < 18){
console.log('You can\'t vote');
}else if(age < 25){
console.log('You can\'t rent a car');
}else{
console.log('You can do anything');
}Trace Output
var people = 30;
var cars = 40;
var buses = 15;
if ( cars > people ){
console.log( "We should take the cars." );
}else if ( cars < people ){
console.log( "We should not take the cars." );
}else{
console.log( "We can't decide." );
}
if ( buses > cars ){
console.log( "That's too many buses." );
}else if ( buses < cars ){
console.log( "Maybe we could take the buses." );
}else{
console.log( "We still can't decide." );
}
if ( people > buses ){
console.log( "All right, let's just take the buses." );
}else{
console.log( "Fine, let's stay home then." );
}Functions
sayHello("Mark");
sayHello("Matt");
function sayHello(name){
console.log('Hello ' + name + '!');
}Functions allow us to create blocks of code that can be run over and over based on some input.
Functions
function sayAge(name, age){
console.log(name + ' is ' + age + ' years old.');
}A function consists of the keyword 'function', then a name(optional), then some arguments.
Functions
console.log(sayAge('Matt', 25));
function sayAge(name, age){
return name + ' is ' + age + ' years old.';
}
//or
function sayAgeTwo(name, age){
var age = name + ' is ' + age + ' years old.';
return age;
}A function can also return a value
Variable Scope
var age = 20;
var name = 'matt';
console.log(sayAge(age));
console.log(result); //undefined
function sayAge(age){
var result = name + ' is ' + age + ' years old.';
return result;
}A variable that is created inside of a function, stays in that function.
Variable Scope
var age = 20;
var name = 'matt';
console.log(sayAge(age));
console.log(result); //same thing as above
function sayAge(age){
result = name + ' is ' + age + ' years old.';
return result;
}Enter the global scope. Global scope is usually bad pratice, because it can pollute the program.
Functions
Turn this into a function...
var age = 22;
if(age < 16){
console.log('You can\'t drive');
}else if(age < 18){
console.log('You can\'t vote');
}else if(age < 25){
console.log('You can\'t rent a car');
}else{
console.log('You can do anything');
}Functions
Turn this into several functions...
var people = 30;
var cars = 40;
var buses = 15;
if ( cars > people ){
console.log( "We should take the cars." );
}else if ( cars < people ){
console.log( "We should not take the cars." );
}else{
console.log( "We can't decide." );
}
if ( buses > cars ){
console.log( "That's too many buses." );
}else if ( buses < cars ){
console.log( "Maybe we could take the buses." );
}else{
console.log( "We still can't decide." );
}
if ( people > buses ){
console.log( "All right, let's just take the buses." );
}else{
console.log( "Fine, let's stay home then." );
}Lesson 3 - Conditionals & Functions
By Mathew Kleppin
Lesson 3 - Conditionals & Functions
Basic Logic and the buildings blocks of programming.
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