unassert - encourage reliable programming by writing assertions in ...

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unassertEncourage Design by Contract (DbC) by writing assertions
in production code, and compiling them away from release
...

Takuto Wada
Twitter: @t_wada
github: @twada

Do you write tests?

assert(typeof item.id === 'strong')
| | | |
| | | false
| | "foo"
| Item{id:"foo",name:"bar"}
"string"
--- [string] 'stron...

Wrestling with Babel6 recently…

unassertEncourage Design by Contract (DbC) by writing assertions
in production code, and compiling them away from release

•unassert
•unassertify
•babel-plugin-unassert
•webpack-unassert-loader
unassert family

'use strict';
var assert = require('assert');
function add (a, b) {
console.assert(typeof a === 'number');
assert(!isNaN(a...

babel --plugins babel-plugin-unassert src.js > dest.js
browserify -t unassertify src.js > dest.js

'use strict';
var assert = require('assert');
function add (a, b) {
console.assert(typeof a === 'number');
assert(!isNaN(a...

User s voice

https://www.mapbox.com/

In internal / private methods, we
check preconditions with assert,
helping us catch mistakes within the
library.
For perfo...

I don't think we should use this
primarily for type checking, but for
preconditions -- parts of API
contracts that cannot ...

Flow & TypeScript are compile-time,
and preconditions could be runtime.
Mapbox GL JS is pretty minimal in
terms of transfo...

preconditions?
postconditions?
invariants?

{P} A {Q}

Design by Contract by Bertrand Meyer

If you promise to call routine with
precondition satisﬁed then I, in
return, promise to deliver a ﬁnal
state in which post...

•redundant checks can and indeed will hurt
•simplicity becomes a crucial criterion
•complexity is the major enemy of quali...

switch (name) {
case 'foo':
doSomething();
break;
case 'bar':
doAnother();
break;
default:
assert(false, 'Cannot be here')...

add(path) {
assert(path instanceof PathElement,
`path should be PathElement but was: ${ typeName(path) }`);
this.paths.pus...

Not only preconditions

What if…
we use power-assert instead of assert?

import assert from 'power-assert';
class Calc {
add (a, b) {
assert(!(isNaN(a) || isNaN(b)));
assert(typeof a === 'number'...

{
"env": {
"development": {
"plugins": [
"babel-plugin-espower"
],
},
"production": {
"plugins": [
"babel-plugin-unassert"...

$ $(npm bin)/babel-node calc.js
AssertionError: # calc.js:5
assert(!(isNaN(a) || isNaN(b)))
| | | | | |
| | | | true NaN
|...

user s voice

One more thing…

unassert is now babel6 ready!

power-assert is not babel6 ready yet
update: 2015/11/13
power-assert now
supports babel6!!

power-assert now works with async/await

# test/some_test.js:6
assert((await bigOrSmall(input)) === big)
| | | |
| | | "big"
"small" 3 false
--- [string] big
+++ [...

Encourage reliable programming
by writing assertions in
production code,
and compiling them away from
release (if you want...

power-assert
https://github.com/power-assert-js/power-assert
unassert
https://github.com/twada/unassert
Thank you!

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