unassert - encourage reliable programming by writing assertions in production
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unassert - Encourage Design by Contract (DbC) by writing assertions in production code, and compiling them away from release. Takuto Wada 2015/11/07 @nodefest Tokkyo 2015
![assert(typeof item.id === 'strong')
| | | |
| | | false
| | "foo"
| Item{id:"foo",name:"bar"}
"string"
--- [string] 'strong'
+++ [string] typeof item.id
@@ -1,6 +1,6 @@
str
-o
+i
ng
I m the author of power-assert-js!
power-assert](https://image.slidesharecdn.com/unassert-nodefest-2015-151109024643-lva1-app6891/75/unassert-encourage-reliable-programming-by-writing-assertions-in-production-4-2048.jpg)
![{
"env": {
"development": {
"plugins": [
"babel-plugin-espower"
],
},
"production": {
"plugins": [
"babel-plugin-unassert"
]
}
}
} .babelrc
unassert in prod, power-assert in dev](https://image.slidesharecdn.com/unassert-nodefest-2015-151109024643-lva1-app6891/75/unassert-encourage-reliable-programming-by-writing-assertions-in-production-27-2048.jpg)
![# test/some_test.js:6
assert((await bigOrSmall(input)) === big)
| | | |
| | | "big"
"small" 3 false
--- [string] big
+++ [string] await bigOrSmall(input)
@@ -1,3 +1,5 @@
-big
+small
power-assert now works with async/await
by @jamestalmage](https://image.slidesharecdn.com/unassert-nodefest-2015-151109024643-lva1-app6891/75/unassert-encourage-reliable-programming-by-writing-assertions-in-production-34-2048.jpg)
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unassert - encourage reliable programming by writing assertions in production
- 1. unassertEncourage Design by Contract (DbC) by writing assertions in production code, and compiling them away from release Takuto Wada Nov 7, 2015 @nodefest Tokyo 2015
- 2. Takuto Wada Twitter: @t_wada github: @twada
- 3. Do you write tests?
- 4. assert(typeof item.id === 'strong') | | | | | | | false | | "foo" | Item{id:"foo",name:"bar"} "string" --- [string] 'strong' +++ [string] typeof item.id @@ -1,6 +1,6 @@ str -o +i ng I m the author of power-assert-js! power-assert
- 5. Wrestling with Babel6 recently…
- 6. unassertEncourage Design by Contract (DbC) by writing assertions in production code, and compiling them away from release
- 8. 'use strict'; var assert = require('assert'); function add (a, b) { console.assert(typeof a === 'number'); assert(!isNaN(a)); assert.equal(typeof b, 'number'); assert.ok(!isNaN(b)); return a + b; } before src.js
- 9. babel --plugins babel-plugin-unassert src.js > dest.js browserify -t unassertify src.js > dest.js
- 10. 'use strict'; var assert = require('assert'); function add (a, b) { console.assert(typeof a === 'number'); assert(!isNaN(a)); assert.equal(typeof b, 'number'); assert.ok(!isNaN(b)); return a + b; } after dest.js
- 11. User s voice
- 13. In internal / private methods, we check preconditions with assert, helping us catch mistakes within the library. For performance, these checks are removed from the production build with unassertify. CONTRIBUTING.md where / when unassert
- 14. I don't think we should use this primarily for type checking, but for preconditions -- parts of API contracts that cannot be statically checked. @jfirebaugh why unassert
- 15. Flow & TypeScript are compile-time, and preconditions could be runtime. Mapbox GL JS is pretty minimal in terms of transforms - envify, brfs, glify - such that all JS is vanilla. @tmcw why not flow / typescript
- 17. {P} A {Q}
- 18. Design by Contract by Bertrand Meyer
- 19. If you promise to call routine with precondition satisfied then I, in return, promise to deliver a final state in which postcondition is satisfied. Design by Contract (DbC)
- 20. •redundant checks can and indeed will hurt •simplicity becomes a crucial criterion •complexity is the major enemy of quality •whose responsibility it is to enforce it: the client's, or the supplier's. Design by Contract (DbC)
- 22. switch (name) { case 'foo': doSomething(); break; case 'bar': doAnother(); break; default: assert(false, 'Cannot be here'); } Not only preconditions
- 23. add(path) { assert(path instanceof PathElement, `path should be PathElement but was: ${ typeName(path) }`); this.paths.push(path); assert.deepEqual(this.paths, sortedPathElements(this.paths), 'this.paths should always be sorted'); } Not only preconditions
- 25. What if… we use power-assert instead of assert?
- 26. import assert from 'power-assert'; class Calc { add (a, b) { assert(!(isNaN(a) || isNaN(b))); assert(typeof a === 'number'); assert(typeof b === 'number'); return a + b; } } const calc = new Calc(); console.log(calc.add(3, NaN)); calc.js write assertions with power-assert
- 27. { "env": { "development": { "plugins": [ "babel-plugin-espower" ], }, "production": { "plugins": [ "babel-plugin-unassert" ] } } } .babelrc unassert in prod, power-assert in dev
- 28. $ $(npm bin)/babel-node calc.js AssertionError: # calc.js:5 assert(!(isNaN(a) || isNaN(b))) | | | | | | | | | | true NaN | false 3 true false power-assert output appears!
- 29. user s voice
- 30. One more thing…
- 31. unassert is now babel6 ready!
- 32. power-assert is not babel6 ready yet update: 2015/11/13 power-assert now supports babel6!!
- 33. power-assert now works with async/await
- 34. # test/some_test.js:6 assert((await bigOrSmall(input)) === big) | | | | | | | "big" "small" 3 false --- [string] big +++ [string] await bigOrSmall(input) @@ -1,3 +1,5 @@ -big +small power-assert now works with async/await by @jamestalmage
- 35. Encourage reliable programming by writing assertions in production code, and compiling them away from release (if you want). to recap