dd-wasm-js-rewriter

Node.js native AST rewriter heavily based on Speedy Web Compiler o SWC compiler used to instrument Javascript source files.

Workflow

1. Parse Javascript code to obtain the AST
2. Replace certain AST expressions -> Currently it is focused in certain operators like + and +=, template literals and some String methods
3. Generate the new Javascript code as from the modified AST -> In addition to the Javascript code, the corresponding source map is returned chaining it with the original source map if necessary.

Usage

``javascript
const Rewriter = require('@datadog/wasm-js-rewriter')

const rewriter = new Rewriter(rewriterConfig)
const result = rewriter.rewrite(code, filename)
`

Configuration options

`javascript

RewriterConfig {
// enable/disable sourceMap chaining - false by default
chainSourceMap?: boolean

// enable/disable comments printing - false by default
comments?: boolean

// establishes the prefix for the injected local variables - 6 random characters by default
localVarPrefix?: string

// sets the list of methods or operators to be rewritten
csiMethods?: Array

// extracts hardcoded string literals - true by default
literals?: boolean
}

CsiMethod {
// name of the String method to rewrite
src: string

// optional name of the replacement method. If not specified a convention shall be used
dst?: string

// indicates if it is an operator like +
operator?: boolean
}
`

Example

`javascript
const Rewriter = require('@datadog/wasm-js-rewriter')

const rewriterConfig = {
csiMethods: [{ src: 'substring' }],
localVarPrefix: 'test',
}

const rewriter = new Rewriter(rewriterConfig)

const code = function sub(a) {
return a.substring(1)
}
const result = rewriter.rewrite(code, filename)

console.log(result.content)
/*
function sub(a) {
let __datadog_test_0, __datadog_test_1;
return (__datadog_test_0 = a, __datadog_test_1 = __datadog_test_0.substring, _ddiast.stringSubstring(__datadog_test_1.call(__datadog_test_0, 1), __datadog_test_1, __datadog_test_0, 1));
}
*/
`

Local setup

To set up the project locally, you should install cargo and wasm-pack:

`
$ curl https://sh.rustup.rs -sSf | sh

$ cargo install wasm-pack
`

and project dependencies:

`
$ npm install
`

$3

Build the project with

`
$ npm run build
`

It will compile WASM binaries by default
and then it will be possible to run the tests with

`
$ npm t
``