zhangchiqing

'use strict';

var R = require('ramda');

// leftPad :: Number -> String -> String
// > leftPad(3, '0', '7')
// '007'
// > leftPad(3, '0', '2016')
// '2016'
var leftPad = R.curry(function(num, fill, str) {

zhangchiqing

// Imperative
function foo(bar) {
  if (!bar) {
    return ;
  } 

  return bar + 1;
}

foo(null);

zhangchiqing

nnoremap <leader>d :call <SID>RunDoctest()<cr>

function! s:RunDoctest()
  if &filetype == "typescript"
    cexpr system('tsc ' . expand('%:p') . '&& doctest --module commonjs ' . substitute(expand('%:p'), ".ts", ".js", ""))
  endif
  if &filetype == "javascript"
    cexpr system('doctest --module commonjs ' . expand('%:p'))
  endif
  copen

zhangchiqing

'use strict';

var R = require('ramda');
var expensiveMap = R.compose(R.join(''), R.repeat(R.__, 10000));

var data = R.range(1, 10000);

// $ time node lazy.js
// node lazy.js  3.42s user 0.16s system 99% cpu 3.584 total
R.take(1, R.map(expensiveMap, data)); 

zhangchiqing

var R = require('ramda');
var Promise = require('bluebird');

var liftP2 = R.curry(function(fn, p1, p2) {
  return Promise.all([p1, p2]).then(R.apply(fn));
});

R.lift(R.add)([1], [2])
// => [3]

zhangchiqing

db.COLLECTION_NAME.aggregate([
  { $match: { created_at: { $gte: ISODate("2016-02-05T00:00:00.000Z"), $lt: ISODate("2016-02-06T00:00:00.000Z") } } }, 
  { $group: { _id: '$FIELD_NAME', count: { $sum: 1 } } }, 
  { $sort: { count: -1 } }
])

zhangchiqing

/*
 * flatMap can be implemented in terms of flatten and map
 * which can be implemented using reduce
 */
'use strict';

// > reduce(function(sum, value) { return sum + value; },
// .   0, [1,2,3])
// 6
var reduce = function(iter, initial, arr) {

zhangchiqing

# npm install --save-dev doctest
# Add "/* doctest */" to the file that contains doctest test cases
# Then use `dt` to run all those test cases
alias dt="git grep '\/\* doctest \*\/' | cut -d ':' -f 1 | xargs ./node_modules/.bin/doctest --module commonjs"

zhangchiqing

# Put the following code into your .bash_profile or .zshrc
local_node_module() {
  ./node_modules/.bin/"$*"
}
alias nn="local_node_module"
# `nn gulp` is now equivalent to `./node_module/.bin/gulp`

zhangchiqing

/* 
 * Example:
 * Find any integer x, y, z that match the following conditions
 *   1. 0 < x < y < z < 10
 *   2. x * x + y * y = z * z
 * In Python:
 *  [(x,y,z) for x in range(1,10) for y in range(1,10) for z in range(1,10) if x < y and y < z and x * x + y * y == z * z]
 *  >>> [(3, 4, 5)]
 * In Javascript with Ramda:
 */