ts-serialize-closures

Serialize your TypeScript functions!

ts-serialize-closures can serialize and deserialize arbitrary TypeScript/JavaScript object graphs. That includes:

• functions, which may have captured data,
• Date and RegExp objects,
• cyclic graphs,
• prototypes,
• references to built-in objects,
• etc.

The idea is that serialize creates a self-contained snapshot of all program state relevant to the object being serialized. The deserialize function decodes that snapshot back to a JavaScript object graph.

This tool might be useful in a number of scenarios:

• Exchanging functions between different processes. That's often a useful tool for building distributed systems.

• Lightweight remote post-mortem debugging: have failing processes create a neat little snapshot of their current state and send yourself that snapshot for analysis.

Usage

The serializer (serialize-closures) requires a preprocessing step (ts-closure-transform). Therefore, the typical usage of this library is to configure webpack to automatically transform the source code using a hook in the TypeScript compiler (tsc). Take the following steps to set up a stand-alone example:

1. Prepare project and install dev-dependencies

mkdir example && cd example
npm init
npm install --save-dev ts-closure-transform serialize-closures webpack webpack-cli typescript ts-loader util

2. Configure webpack.config.js:

const tsClosureTransform = require('ts-closure-transform');
const path = require('path');
module.exports = {
  entry: {
    example: './src/example.ts',
  },
  module: {
    rules: [
      {
        test: /.tsx?$/,
        loader: 'ts-loader', // or 'awesome-typescript-loader'
        options: {
          getCustomTransformers: () => ({
            before: [tsClosureTransform.beforeTransform()],
            after: [tsClosureTransform.afterTransform()]
          })
        }
      }
    ]
  },
  resolve: {
    extensions: [ '.tsx', '.ts', '.js' ],
    fallback: {
      "util": require.resolve("util/"),
    },
  },
  output: {
    path: path.join(__dirname, 'dist'),
    filename: '[name].bundle.js',
  }
}

3. Write code to serialize and deserialize arbitrary functions:

import { serialize, deserialize } from 'serialize-closures';
// Just about anything can be serialized by calling `serialize`.
let capturedVariable = 5;
let serialized = serialize(() => capturedVariable);

// Serialized representations can be stringified and parsed.
let text = JSON.stringify(serialized);
let parsed = JSON.parse(text);

// Serialized representations can be deserialized by calling `deserialize`.
console.log(deserialize(serialized)()); // Prints '5'.
console.log(deserialize(parsed)());     // Prints '5'.

4. Compile with webpack and run the sample

npx webpack
node dist/example.bundle.js

Components

The serializer consists of two components.

1. ts-closure-transform: a transformation to inject in the TypeScript compiler's pass pipeline. This transformation will rewrite all function definitions to include a special __closure property. The serializer uses that __closure property to figure out which variables are captured by the function.

   How you inject this transform depends on the webpack loader you're using. For ts-loader and awesome-typescript-loader, you can do the following:

   import { beforeTransform, afterTransform } from 'ts-closure-transform';
   // ...
   loader: 'ts-loader', // or 'awesome-typescript-loader'
   options: {
     getCustomTransformers: () => ({
       before: [beforeTransform()],
       after: [afterTransform()]
     })
   }
   // ...

   Note that ts-closure-transform is strictly a dev dependency: there's no need to package it with your application.

2. serialize-closures: a runtime library that defines the serialize and deserialize functions. These should work for any object graph as long as all source code has first been processed by ts-closure-transform.

Limitations

ts-serialize-closures works fairly well for modest object graphs, but it does have a number of limitations you should be aware of:

• Variable-capturing functions defined in files that have not been transformed by ts-closure-transform cannot be deserialized correctly.

• Serializing class definitions works, but only if they are first lowered to function definitions by the TypeScript compiler, i.e., the target is ES5 or lower.

• Functions can only be serialized and deserialized once. There is no support for serializing a deserialized function.