# Angular Build Optimizer

Angular Build Optimizer contains Angular optimizations applicable to JavaScript code as a TypeScript transform pipeline.


## Available optimizations

Transformations applied depend on file content:

- [Class fold](#class-fold), [Scrub file](#scrub-file) and [Prefix functions](#prefix-functions): applied to Angular apps and libraries.
- [Import tslib](#import-tslib): applied when TypeScript helpers are found.

Non-transform optimizations are applied via the [Purify Plugin](#purify-plugin).

Some of these optimizations add `/*@__PURE__*/` comments.
These are used by [UglifyJS](https://github.com/mishoo/UglifyJS2) to identify pure functions that can potentially be dropped.


### Class fold

Static properties are folded into ES5 classes:

```typescript
// input
var Clazz = (function () { function Clazz() { } return Clazz; }());
Clazz.prop = 1;

// output
var Clazz = (function () { function Clazz() { } Clazz.prop = 1; return Clazz; }());
```


### Scrub file

Angular decorators, property decorators and constructor parameters are removed, while leaving non-Angular ones intact.

```typescript
// input
import { Injectable, Input } from '@angular/core';
import { NotInjectable } from 'another-lib';
var Clazz = (function () { function Clazz() { } return Clazz; }());
Clazz.decorators = [{ type: Injectable }, { type: NotInjectable }];
Clazz.propDecorators = { 'ngIf': [{ type: Input }] };
Clazz.ctorParameters = function () { return [{type: Injector}]; };

// output
import { Injectable, Input } from '@angular/core';
import { NotInjectable } from 'another-lib';
var Clazz = (function () { function Clazz() { } return Clazz; }());
Clazz.decorators = [{ type: NotInjectable }];
```


### Prefix functions

Adds `/*@__PURE__*/` comments to top level downleveled class declarations and instantiation. 
Webpack library imports are also marked as `/*@__PURE__*/` when used with [Purify Plugin](#purify-plugin).

```typescript
// input
var Clazz = (function () { function Clazz() { } return Clazz; }());
var newClazz = new Clazz();
var newClazzTwo = Clazz();

// output
var Clazz = /*@__PURE__*/ (function () { function Clazz() { } return Clazz; }());
var newClazz = /*@__PURE__*/ new Clazz();
var newClazzTwo = /*@__PURE__*/ Clazz();
```


### Import tslib

TypeScript helpers (`__extends/__decorate/__metadata/__param`) are replaced with `tslib` imports whenever found.

```typescript
// input
var __extends = (this && this.__extends) || function (d, b) {
  for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
  function __() { this.constructor = d; }
  d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};

// output
import { __extends } from "tslib";
```


### Purify Plugin

Performs regex based replacements on all files that add `/*@__PURE__*/` comments to downleveled classes,  TypeScript 
enums and webpack imports (used with [Prefix functions](#prefix-functions))


## Library Usage

```typescript
import { buildOptimizer } from '@angular-devkit/build-optimizer';

const transpiledContent = buildOptimizer({ content: input }).content;
```

Available options:
```typescript
export interface BuildOptimizerOptions {
  content?: string;
  inputFilePath?: string;
  outputFilePath?: string;
  emitSourceMap?: boolean;
  strict?: boolean;
}
```


## Webpack loader and plugin usage:

```typescript
const PurifyPlugin = require('@angular-devkit/build-optimizer').PurifyPlugin;

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        loader: '@angular-devkit/build-optimizer/webpack-loader'
        options: {
          sourceMap: false
        }
      }
    ]
  },
  plugins: [
    new PurifyPlugin()
  ]
}
```


## CLI usage

```bash
build-optimizer input.js
build-optimizer input.js output.js
purify input.js
purify input.js output.js
```