Add flow typings

.babelrc

@@ -1,5 +1,6 @@
 {
   "presets": [
+    "flow",
     "env"
   ]
 }

.flowconfig

@@ -0,0 +1,9 @@
+[ignore]
+
+[include]
+
+[libs]
+
+[lints]
+
+[options]

lib/index.js

@@ -58,4 +58,4 @@ function wilsonInterval(proportion, sample, zScore) {
     center: center,
     low: low
   };
-}
+}

package.json

@@ -28,11 +28,13 @@
   "main": "./lib/index.js",
   "scripts": {
     "dev": "npm run build -- --watch & npm test -- --watchAll & wait",
-    "build": "babel ./src/index.js --out-file ./lib/index.js",
+    "build": "babel src -d lib --ignore test.js",
+    "flow": "flow",
     "test": "jest --coverage",
     "test-ci": "jest --coverage && cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js",
     "lint": "eslint src",
-    "precommit": "npm run lint && npm run test && npm run build && git add lib"
+    "precommit": "npm run lint && npm run test && npm run build && git add lib",
+    "prepublish": "npm run build"
   },
   "dependencies": {
     "mathjs": "^3.15.0",
@@ -43,10 +45,12 @@
     "babel-eslint": "^7.2.3",
     "babel-jest": "^20.0.3",
     "babel-preset-env": "^1.6.0",
+    "babel-preset-flow": "^6.23.0",
     "coveralls": "^2.13.1",
     "eslint": "^4.3.0",
     "eslint-plugin-babel": "^4.1.2",
     "eslint-plugin-jest": "^20.0.3",
+    "flow-bin": "^0.52.0",
     "husky": "^0.14.3",
     "jest": "^20.0.4"
   }

src/index.js

@@ -1,7 +1,7 @@
 import math from 'mathjs';
 import pnormaldist from 'pnormaldist';
 
-export default function wilson(observed, sample, population = false, options = {}) {
+export default function wilson(observed: number, sample: number, population = false, options = {}) {
   const {
     confidence = 0.95,
     precision = 20,