强类型 JavaScript 的解决方案

x = 5; // 5
x = x + 'A'; // '5A'

$ npm install -g typescript

// greet.ts
function greet(person: string) {
  console.log("Hello, " + person);
}
greet([0, 1, 2]);

$ tsc greeter.ts
greet.ts(5,9): error TS2345: Argument of type 'number[]'   
is not assignable to parameter of type 'string'.

$ npm install -g flowcheck

function sum(a: number, b: number) {
  return a + b;
}
sum('hello','world')

$ browserify -t flowcheck -t [reactify --strip-types] \
input.js -o output.js

var _f = require("flowcheck/assert");
function sum(a, b) {
    _f.check(arguments, _f.arguments([_f.number, _f.number]));
  return a + b;
}

$ node output.js
// throw new TypeError(message);
            ^
TypeError: 
Expected an instance of number got "hello",   
context: arguments / [number, number] / 0
Expected an instance of number got "world",  
context: arguments / [number, number] / 1

$ npm install --global flow-bin

// hello.js
/* @flow */
function foo(x) {
  return x*10;
}
foo("Hello, world!");

$ flow check
hello.js:7:5,19: string
This type is incompatible with
/hello.js:4:10,13: number

/* @flow */
function foo(x: string, y: number): string {
  return x.length * y;
}
foo("Hello", 42);

// annotation.js
/**
  @param {number} x
  @return {number}
 */
function square(x) {
  return x * x;
}
square(5);

$ flow port annotation.js
function square(x: number) : number {
   return x * x;
 }