Remove the Boilerplate
Gleb Bahmutov
KENSHO
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed vulputate, orci non porta dignissim, ipsum neque hendrerit neque, in molestie metus dolor quis erat. Sed semper sit function orci sed sagittis. Nulla ut ultricies arcu, eu rutrum nisi. In hac habitasse platea dictumst. Ut vel add (tellus. Ut a, suscipit b) diam interdum tortor tincidunt, { eu consectetur leo efficitur. Proin return a + b; tortor nisi, dignissim eu porta non, auctor in nisi. Cras suscipit augue nec felis ornare, non } elementum dolor blandit. Vestibulum auctor commodo nunc, id interdum ex auctor eu. Vivamus gravida interdum viverra. Nunc porta sodales ipsum, a tempus leo placerat vel. Quisque ut massa id elit facilisis porttitor at efficitur velit.
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed vulputate, orci non porta dignissim, ipsum neque hendrerit neque, in molestie metus dolor quis erat. Sed semper sit function orci sed sagittis. Nulla ut ultricies arcu, eu rutrum nisi. In hac habitasse platea dictumst. Ut vel add (tellus. Ut a, suscipit b) diam interdum tortor tincidunt, { eu consectetur leo efficitur. Proin return a + b; tortor nisi, dignissim eu porta non, auctor in nisi. Cras suscipit augue nec felis ornare, non } elementum dolor blandit. Vestibulum auctor commodo nunc, id interdum ex auctor eu. Vivamus gravida interdum viverra. Nunc porta sodales ipsum, a tempus leo placerat vel. Quisque ut massa id elit facilisis porttitor at efficitur velit.
var add = function (a, b) {
return a + b;
};4 entities: a, b, add and a function
Each entity can interact with other 3
Kensho Node
var add = function (a, b) {
return a + b;
};for N entities: N * (N - 1) interactions
Kensho Node
Human brain has limit: 3 - 7 things at a time
Errors = more * code^2
E = m * c^2
Kensho Node
function add(a, b) {
return a + b;
}Removed unnecessary variable add
Kensho Node
Goal: replace the boilerplate with equivalent short and readable code
Kensho Node
Tools: ES5, FP, ES6
Kensho Node
Balance: readability, testability, performance
Example
var path = require('path');
var first = path.join(__dirname, '../foo');
...
var second = path.join(__dirname, '../bar');Kensho Node
Example
var join = require('path').join;
var first = join(__dirname, '../foo');
...
var second = join(__dirname, '../bar');Kensho Node
Example
var relativePath = require('path')
.join.bind(null, __dirname);
var first = relativePath('../foo');
...
var second = relativePath('../bar');Kensho Node
Example
var first = path.join(__dirname, '../foo');
// vs
var second = relativePath('../bar');Kensho Node
- functional programming
- promises
- helpers for unit tests
Partial application
var relativePath = path.join.bind(null, __dirname);
relativePath('foo.js');Functional programming
Kensho JavaScript
function fn(a, b, c) { ... }
var newFn = fn.bind(null, valueA, valueB);
newFn(valueC);Partial application
Kensho JavaScript
Place on the left arguments that are likely to be known first
function fn(a, b, c) { ... }
var newFn = fn.bind(null, valueA, valueB);
newFn(valueC);Design the signatures
Kensho JavaScript
function updateUserInfo(userId, newInfo){ ... }
// vs
function updateUserInfo(newInfo, userId){ ... }Example
Kensho JavaScript
// user-service.js
function updateUserInfo(userId, newInfo) { ... }
// user-controller.js
var updateUser;
function onLogin(id) {
updateUser = updateUserInfo.bind(null, id);
}Example
Kensho JavaScript
$('form').on('submit', function onSubmitted(form) {
updateUser(form);
});Partial application from the left
function fn(a, b, c) { ... }
var newFn = fn.bind(null, valueA, valueB);Kensho Lodash and Ramda
// or
var _ = require('lodash');
var newFn = _.partial(fn, valueA, valueB);
// or
var R = require('ramda');
var newFn = R.partial(fn, valueA, valueB);Partial application from the right
['1', '2', '3'].map(parseInt); // [1, NaN, NaN]// function parseInt(x, radix)
// but Array.map sends (value, index, array)
['1', '2', '3'].map(function (x) {
return parseInt(x, 10);
});['1', '2', '3'].map(_.partialRight(parseInt, 10));
// [1, 2, 3]
// radix is bound,
// index and array arguments are ignoredKensho Lodash and Ramda
Partial application with placeholders
// function parseInt(x, radix)
['1', '2', '3'].map(_.partial(parseInt, _, 10));
// [1, 2, 3]// or
var S = require('spots');
['1', '2', '3'].map(S(parseInt, S, 10));
// [1, 2, 3]Kensho Lodash and Ramda
Example: routing placeholders
// Express
// same callbacks to check if the user is logged in and authorized
app.get('/repos',
passport.isAuthenticated, passport.isAuthorized, ctrl.getRepos);
app.get('/repos/:user/:name',
passport.isAuthenticated, passport.isAuthorized, ctrl.getRepo);
app.get('/repos/view/:user/:name',
passport.isAuthenticated, passport.isAuthorized, ctrl.viewFile);app.get(<url>, passport.isAuthenticated, passport.isAuthorized, ...);Kensho Lodash and Ramda
Example: routing placeholders
// prefill 2 middle arguments using spots
var S = require('spots');
var authGet = S(app.get, S,
passport.isAuthenticated, passport.isAuthorized)
.bind(app);
// authGet(<url>, <controller>)authGet('/repos', ctrl.getRepos);
authGet('/repos/:user/:name', ctrl.getRepo);
authGet('/repos/view/:user/:name', ctrl.viewFile);Kensho Lodash and Ramda
Partial application by name
// divide by 10
function divide(a, b) { return a / b; }
var selective = require('heroin');
var by10 = selective(divide, { b: 10 });
console.log(by10(10)); // 1 (a = 10, b = 10)
console.log(by10(2)); // 0.2 (a = 2, b = 10)Kensho Lodash and Ramda
Partial application by key
function fn(options) { ... }
var obind = require('obind');
var withBar = obind(fn, { bar: 'bar' });
withBar({ baz: 'baz' });
/*
equivalent to
foo({
bar: 'bar',
baz: 'baz'
})
*/Kensho Lodash and Ramda
Working with arrays without boilerplate
var numbers = [3, 1, 7];
var constant = 2;
var k = 0;
for(k = 0; k < numbers.length; k += 1) {
console.log(numbers[k] * constant);
}
// 6 2 14Kensho Node
Use ES5 methods
function mul(a, b) {
return a * b;
}
function print(n) {
console.log(n);
}
numbers.map(function (n) {
return mul(n, constant);
}).forEach(print);
// 6 2 14Kensho Node
Use ES5 methods
function mul(a, b) {
return a * b;
}
var byK = mul.bind(null, constant);
var print = console.log.bind(console);
numbers
.map(byK)
.forEach(print);Kensho Node
pointfree style
Use ES5 methods
function mul(a, b) {
return a * b;
}
var byK = mul.bind(null, constant);
var print = console.log.bind(console);
numbers
.map(byK)
.forEach(print);Kensho Node
pointfree style
Use Lodash
var numbers = [3, 1, 7];
var constant = 2;
function mul(a, b) {
return a * b;
}
var _ = require('lodash');
var byK = _.partial(mul, constant);
var print = _.bind(console.log, console);
_.forEach(_.map(numbers, byK), print);Kensho Node
var mul = _.curry(function (a, b) {
return a * b;
});
var byK = mul(constant);function mul(a, b) {
return a * b;
}
var byK = _.partial(mul, constant);Curried functions have partial application built in.
Kensho Node
Order of arguments
function cb(item, index, array) { ... }
// ES5 method
Array.prototype.map(cb);
// Lodash method
_.map(array, cb);Place on the left arguments that are likely to be known first
Kensho API design
Ramda library
var R = require('ramda');
// callback is first argument
R.map(cb, array);// all functions are curried
var by5 = R.multiply(5);
by5(10); // 50Kensho API design
Multiply then print
var printAll = R.forEach(print);
printAll(multiplyAll(numbers));Kensho API design
var numbers = [3, 1, 7];
var constant = 2;
var R = require('ramda');
var print = R.bind(console.log, console);
var multiplyAll = R.map(R.multiply(constant));Pointfree allows composition
var multiplyAll = R.map(R.multiply(constant));
var printAll = R.forEach(print);
printAll(multiplyAll(numbers));Kensho FP
f(g(x)) = (f \circ g)(x)
Compose
var multiplyAll = R.map(R.multiply(constant));
var printAll = R.forEach(print);
var computation = R.compose(printAll, multiplyAll);
computation (numbers);Static logic
Dynamic data
Kensho FP
R.pipe and R.tap
var mulPrint = R.pipe(
R.map(R.multiply(constant)),
R.tap(debugLog),
R.forEach(R.bind(console.log, console))
)
mulPrint (numbers)R.pipe for readability
R.tap for debugging
Kensho FP
Asynchronous code
var glob = require('glob');
function getJavaScriptFiles(cb) {
glob('*.js', function (err, files) {
if (err) {
return cb(err);
}
cb(null, files);
});
}
getJavaScriptFiles(function (err, files) {
if (err) {
return console.error(err);
}
console.log(files);
});Kensho Promises
Promises
var getJavaScriptFiles = require('q')
.denodeify(require('glob'))
.bind(null, '*.js');getJavaScriptFiles()
.then(console.log)
.catch(console.error)
.done();Kensho Promises
No more error handling or callback boilerplate
Start without boilerplate
var Q = require('q');
function asyncF() {
var defer = Q.defer();
process.nextTick(function () {
defer.resolve('f');
});
return defer.promise;
}Q('f')
// or
Promise.resolve('f')Kensho Promises
.then without boilerplate
promise
.then(function (x) {
return new Promise(function (resolve) {
resolve(x + 1)
})
})Kensho Promises
promise
.then(function (x) {
return x + 1
})
// or
promise.then(R.inc)Use "tap" to inspect value
Kensho Promises
promise
...
.then(function (x) {
console.log(x)
return x
})promise
...
.then(R.tap(console.log))Promise composition
Q(...)
.then(R.inc)
.then(R.tap(console.log))
.then(verify)
.done()var printThenVerify = R.pipeP(
R.inc,
R.tap(console.log),
verify
)
Q(...)
.then(printThenVerify)
.done()Kensho Promises
Use promise library API
fs.readdirAsync('.')
.map(processFile, { concurrency: 3 })
.then(fileResults);Kensho Promises
Advanced: generators, async / await, reactive streams
Kensho RxJS
Remove boilerplate from unit tests
Use a better framework
QUnit.test('a test', function(assert) {
var done = assert.async();
asyncOperation()
.then(function () {
// assert something
done();
});
});Kensho testing
Use a better framework
// Mocha
it('works', function (done) {
asyncOperation()
.then(function () {
// assert something
done();
});
});Kensho testing
Use a better framework
// Mocha
it('works', function () {
return asyncOperation()
.then(function () {
// assert something
});
});Kensho testing
Write a test wrapper
// typical AngularJS unit test
describe('typical test', function () {
var $rootScope, foo;
beforeEach(function () {
angular.mock.module('A');
// other modules
});
beforeEach(inject(function (_$rootScope_, _foo_) {
$rootScope = _$rootScope_;
foo = _foo_;
}));
it('finally a test', function () {
$rootScope.$apply(); // for example
expect(foo).toEqual('bar');
});
});Kensho OSS
Write a test wrapper
ngDescribe({
modules: 'A',
inject: 'foo',
tests: function (deps) {
it('finally a test', function () {
deps.step()
expect(deps.foo).toEqual('bar')
})
})
})Kensho OSS
Boilerplate in assertions
it('does something', function () {
...
expect(foo).toEqual('bar');
});
test "does something" failed
Error:What has actually failed and why?
Kensho defensive code
Boilerplate in assertions
it('does something', function () {
...
expect(foo).toEqual('bar',
'expected foo to equal "bar"');
});
test "does something" failed
Error: expected foo to equal "bar"Why did it fail?
Kensho defensive code
Boilerplate in assertions
it('does something', function () {
...
expect(foo).toEqual('bar',
'expected foo ' + foo + ' to equal "bar"');
});
test "does something" failed
Error: expected foo something to equal "bar"Message repeats the predicate!
Kensho defensive code
Boilerplate in assertions
it('does something', function () {
...
expect(foo).toEqual('bar',
'expected foo ' + JSON.stringify(foo) +
' to equal "bar"');
});Kensho defensive code
Lazy assertions
// require('lazy-ass');
it('does something', function () {
la(foo === 'bar',
'expected foo', foo, 'to equal "bar"');
});Kensho defensive code
Test helper
var helpfulDescribe = require('lazy-ass-helpful');
helpfulDescribe(function tests() {
it('does something', function () {
la(foo === 'bar');
});
});Kensho defensive code
JS engine executes
var helpfulDescribe = require('lazy-ass-helpful');
helpfulDescribe(function tests() {
it('does something', function () {
la(foo === 'bar',
'condition [foo === "bar"], foo is', foo);
});
});Kensho defensive code
lazy-ass-helpful rewrites code using falafel
Boilerplate and ES6
// ES5: need all arguments after "y"
function f(x, y) {
var a = Array.prototype.slice.call(arguments, 2);
...
};// using lodash
function f(x, y) {
// need all arguments after "y"
var a = _.toArray(arguments).slice(2);
...
};Kensho ES6
Boilerplate and ES6
// ES5: need all arguments after "y"
function f(x, y) {
var a = Array.prototype.slice.call(arguments, 2);
...
};// using ES6 Array.from
function f(x, y) {
// need all arguments after "y"
var a = Array.from(arguments).slice(2);
...
};// using ES6 rest parameter
function f(x, y, ...a) {
// a is an array of arguments after "y"
...
};Kensho ES6
ES6 default values
function f (x, y, z) {
if (y === undefined)
y = 7;
if (z === undefined)
z = 42;
return x + y + z;
};// es6
function f (x, y = 7, z = 42) {
return x + y + z
}Kensho ES6
ES6 computed keys
var foo = '...';
var o = {};
o[foo] = 42;// es6
var foo = '...';
var o = {
[foo]: 42
}Kensho ES6
ES6 arrow functions
numbers.map(function (v) { return v + 1; });
// es6
numbers.map(v => v + 1);// I prefer
var R = require('ramda');
var add1 = R.add(1);
numbers.map(add1);Kensho ES6
Conclusions
- Small reusable functions
- Design signatures for partial application
- Combine functions into pipelines
- Use promises
- Deal with boilerplate in your unit tests
Kensho Node
Remove the Boilerplate
KENSHO