Week 5 java script functions

Speaking in Code

Intro to JavaScript
Functions!

Brian Lee

Professor Liel Leibovitz

Speaking in Code

Logistics

• Spring Break – no class next week

Speaking in Code

Big Picture: HTML/CSS vs. JavaScript

• HTML/CSS are computer languages that define
content, structure, and how things look

• JavaScript is a programming language where you give
the computer instructions
– Set of directions such as for recipes

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Big Picture: Programming

• Learning JavaScript – programming language

• Widely-applicable concepts

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Programming Language Similarities
• JavaScript
if (x < 10) {
console.log("x is less than 10!");
}

• Ruby
if x < 10
puts "x is less than 10!"

• Python
if x < 10:
print "x is less than 10!"

Speaking in Code

Programming Language Similarities
• JavaScript
if (x < 10) {
console.log("x is less than 10!");
}

• Java
if(x < 10)
{
System.out.println("x is less than 10!");
}

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Big Picture: What we’re learning now

• Using JavaScript to tell browser what to do

• “Front-end” language

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Big Picture: How it all fits in (HTML)

<!DOCTYPE html>
<html>
<head>
<title>HTML title</title>
</head>
<body>
<p>paragraph</p>
</body>
</html>

Speaking in Code

Big Picture: How it all fits in (CSS)

<!DOCTYPE html>
<html>
<head>
<link type="text/css" rel="stylesheet" href="stylesheet.css"/>
</head>
<body>
<p id=“color-me”>paragraph</p>
</body>
</html>

Speaking in Code

Big Picture: How it all fits in (JavaScript)

<!DOCTYPE html>
<html>
<head>
<link type="text/css" rel="stylesheet" href="stylesheet.css"/>
<script type="text/javascript" src="script.js"></script>
</head>
<body>
<p id=“color-me”>paragraph</p>
</body>
</html>

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JavaScript

• Each line is read one at a time

• Comments
// These won’t be read in JavaScript

• Most lines are ended with ;
– Like a period at the end of a sentence

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JavaScript

• Print to the screen (console)

console.log(‘Hello World’);
console.log(9482301);

• Try it in your browser console
– Right-click -> Inspect Element -> Console

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Recap: Types
• Everything is associated with a type
• Numbers
254

• Strings
“Hi there!”

• Booleans
true
false

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Recap: Types – Strings

• You can concatenate strings

“Brian” + “ Lee”
>> Brian Lee

“1” + “ 1”
>> “11”

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Recap: Conditionals

• Arithmetic expressions compute to a Number
4 * 5;
>> 20

• Conditionals compute to a Boolean
20 > 15;
>> true

13 >= 15;
>> false

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Recap: Conditionals

• Operators

>
<
>=
<=
===

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Recap if statements

• Execute code based on a set of conditions

• English: If you are older than 21, then you can drink

• JavaScript: (try in JSbin)
var i = 18;
if ( i >= 21) {
console.log(“you can drink!”);
}else {
console.log(“better wait another year”);
}

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Variables

• Very similar to variables in algebra
• Begin with var to instantiate

var firstName = “Brian”
var lastName = “Lee”
console.log(firstName + “ “ + lastName)
>> “Brian Lee”

• Common practice to camelCase

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Variables

• Should be lowercase first (otherwise Objects)

• Cannot start with numbers, no spaces

var 1stName = “Brian”
var LastName = “Lee”

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Common Gotchas
• Important:
var taxRate = 1.089;
var tax rate = 1.089; //error no spaces between variable names
vartaxRate = 1.089; //error need space between var and variable name

• Not as important
if(10 > 5) { console.log("Hello!"); }

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Indenting

• Similar to the principals for HTML

• Makes it easier for you!

• No set standard, but just stick to it!
var i = 18;
if (i >= 21) {
console.log(‘you can drink!’);
}else {
console.log(‘better wait another year’);
}

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Gotcha’s: Read line by line

• This won’t work:

var cost = 24.99;
var total = cost * taxRate;

Speaking in Code

Intro to Functions: Name

• No need to repeat same code

• Set of instructions

var drinking = function(age) {
if (age >= 21) {
}else {
}
};

drinking(21);

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Intro to Functions: Syntax



if (age >= 21) {
}else {
}
};

drinking(21);

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Intro to Functions: Parameters



if (age >= 21) {
}else {
}
};

drinking(21);

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Functions === Microwave Buttons?

• Each button has a purpose

Speaking in Code

Functions === Microwave Buttons?

• Each button has a purpose

• Same as a function
var minutes = 5
var addTime = function(minutes, additionalMinutes) {
minutes = minutes + additionalMinutes;
return minutes;
};

addTime(minutes, 10);
>> 15

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Try it yourself

http://bit.ly/jsfunctions

http://jsbin.com

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Sync-Up!

• Using return

var minutes = 5
var addTime= function(minutes, additionalMinutes) {
return minutes;
};

console.log(addTime(minutes, 10) + 2);
>> 17

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Sync-Up!

• Using return

var minutes = 5
var addTime= function(minutes, additionalMinutes) {
return minutes;
};

console.log(15 + 2);
>> 17

Speaking in Code

Sync-Up!

• Calling functions: Name

if (age >= 21) {
}else {
}
};
drinking(21);
drinking(18);
drinking(25);

Week 5 java script functions

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