freeCodeCamp Tokyo meetup 19 2016/08/31 @ Fork Inc.

1. freeCodeCamp Tokyo
#19 2016/08/31
@ Fork Inc.
Welcome to freeCodeCamp
Tokyo meetup!

2. Who am I?
Tanoue Kenta
Web Programmer
Ruby on Rails
React
“Less is more”

3. What is freeCodeCamp?

4. Today's schedule
19:15~ Opening
19:25~ Pair programming
20:00~ Presentation
20:15~ Drinking party 🍺 (fee: 500 yen)

5. Pair programming
Design quality Learning
Two programmers work together at
one workstation.
One, the driver, writes code
while the other, the navigator,
reviews each line of code as it is
typed in.
https://en.wikipedia.org/wiki/Pair_programming

6. Better code (in my opinion)
Readability
Maintainability
var i = 5
What does “i” variable means?
function calMaxAndExcludeOddNumbersInArr(arr)
Too many roles!

7. Modern Javascript (ES2015)
Better code part2
https://github.com/metagrover/ES6-for-humans
https://babeljs.io/docs/learn-es2015/
Arrows
var plus = (x, y) => { return x + y; };
Classes
class Human {
constructor(name) { this.name = name; }
}
Array Spread
function f(x, ...y) {
return x * y.length;
}
f(3, "hello", true) == 6

8. • Array Map, Filter, Reduce (Functional Programming)
Better code part3
Map Filter Reduce
Array Map, Filter and Reduce in JS | Aten Design Group http://atendesigngroup.com/blog/array-map-filter-and-reduce-js

9. Strange behavior in
Javascript numbers
var x = 9999999999999999;
x will be 10000000000000000

10. Strange behavior in
Javascript numbers
var x = 0.2 + 0.1;
x will be 0.30000000000000004

11. Why?
JavaScript Numbers are always 64-bit Floating Point
https://en.wikipedia.org/wiki/IEEE_754-1985

12. Solutions
• var x = (0.2 * 10 + 0.1 * 10) / 10;
• use math.js library http://mathjs.org/index.html

13. Javascript data types
• Six data types that are primitives:
• Boolean
• Null
• Undefined
• Number
• String
• Symbol (new in ECMAScript 6)
• and Object

14. What is type of Date?
typeof( Date.now() );
Numbers(Unix Timestamp)
ex) 1472635026140

15. Today’s challenge
Exact Change
https://www.freecodecamp.com/challenges/exact-change
ONE HUNDRED: 100.0$
TWENTY: 20.0$
TEN: 10.0$
FIVE: 5.0$
ONE: 1.0$
QUARTER: 0.25$
DIME: 0.1$
NICKEL: 0.05$
PENNY: 0.01$

16. Have a nice code!

17. sample code
https://gist.github.com/regonn/
1ffb5a71e61d569bedd98f7ac58fcef3