Add polyfill code

[markandey]

What ?

This Pull Request contains reviewable code from Intl.DateTimeFormat timezone polyfill.

How

Code Files

Polyfill code is split across 3 files.

1. polyfill.js
2. lookup-utill.js
3. data-loader.js

src/code/polyfill.js

This contains polyfill code. i.e. in this file you would see prototype of Intl.DateTimeFormat and Date is modified to achieve polyfill.

src/code/lookup-utill.js

This file contains functions to get access to timezone data and locale data. To achieve DateTime formatting.

src/code/data-loader.js

This file contains functions unpack data from data file and loads into memory.

Data Files

1. src/data/timezones/tzdata-america-los_angeles.js
   This data is downloaded from iana
2. If Multiple timezone have same definitions they are deduped, into one.
3. All untill timeStamps are indexed in an array.
4. All offset is index in an rray
5. isDst is represented as it is.
6. All indeices and values in index array are base 32 strings.

   "America/Los_Angeles||0,0,0,1,1,1,2,0,0,3,1,1,4,0,0,5,1,1,6,1,1,7,0,0,8,1,1
   ---^--------------------^-^-^--------------------------------------------
   --timezone------------[untill32]-[offset32]--isdst---
 ------------------------timeStamps---offsets-----------------------------

1. src/data/locales/locale-en-US-POSIX.js
   This is transformation of CLDR data.
   Compression is achieved by indexing the words in zoneNameIndex array and for every metaZone providing 4 values for shortStandard, shortDayLight, longStandard, longDayLight. separated by | and every word is separated by , . zoneNameIndex is sorted by words' frequency so that high frequency words represented by small number.
   e.g.

"Samoa": "30,0,2,0,1|30,0,4,0,1||",
--^--------^-----------^------ --^              

[yahoocla]

CLA is valid!

[markandey]

@jlecomte @juandopazo

[jlecomte]

I would use the es2015 preset in your `.babelrc'. Also, I suggest you use the same eslint config we use for our internal projects, to ensure consistent and strict code styling. I noticed your test files use tabs, but your source files use 4 white spaces for indentation. Please be consistent across the repo (4 white spaces) I will do another review when all these concerns have been addressed. Thanks!

[jlecomte]

Shouldn't we throw here?

[jlecomte]

Usually, this is done as part of the while statement above...

[jlecomte]

Shouldn't we throw here?

[jlecomte]

What's Ob? If we throw instead of using console.warn, this is true. Otherwise, it's incorrect since the function can return undefined...

[jlecomte]

Missing extra line at the end...

[jlecomte]

Use const or let on each line...

[jlecomte]

Use const or let on each line...

[jlecomte]

Use const or let on each line...

[jlecomte]

Use const or let on each line...

[jlecomte]

Remove "Returns" :)

[markandey]

@jlecomte Addressed them all.

[juandopazo]

parseInt(x, 32) 😮

[markandey]

Yes data files contains index and timestamp values as base32 represented strings.
I guess You mean, why base is 32 and not 10 ??

[juandopazo]

If you're ever concerned about the performance of this code, this is doing a lot of mutations, where you could just be having a while loop where you increment a counter by 3...

let result = [], i = 0;
while (i < arr.length) {
  result.push([arr[i], arr[i + 1], arr[i + 2]);
  i += 3;
}

And it wouldn't be harder to understand.

[juandopazo]

Overall, I really wish there were more comments everywhere. There's a lot of code that is based on some internal conventions and data structure, so anyone looking at it would have a hard time following it. Some well placed comments would help a lot.

[markandey]

@juandopazo @jlecomte

1. Added lot of comments all around.
2. Polyfill class now inherits original class , which makes instanceof test pass.

[jlecomte]

@markandey I skimmed the repo and this PR. Overall, it looks fine to me 👍 but I will let @juandopazo do one final pass.

[markandey]

@juandopazo I did test that static functions are preserved from original Intl.DateTimeFormat.
Lets get this merged to proceed !

[juandopazo]

@markandey I took a second look. Overall looks much better! There's still a few issues I noted inline. After those, let's merge this and make it public so we can get some feedback from the community.