Flinject - Typed function injector

Inject any code into any function without worrying about types.

👉 Simple example

import inject from 'flinject'

self.eval = inject(self.eval, () => console.log('Eval used!'))

👍 Useful example

import inject from 'flinject'

Buffer.alloc = inject(Buffer.alloc, ({ target, stacktrace }, size) => {
  if(size < 1024) return
  const at = stacktrace[0]
  console.log(`WARNING: Trying to allocate buffer larger than 1024 with (${size} bytes)\n At: ${at.getFileName()} ${at.getLineNumber()}:${at.getColumnNumber()}`)
  return target(1024) // Use `target` instead of original function( e.g. Buffer.alloc ) to avoid stack overflow
})

const buf = Buffer.alloc(1025) // Trying to allocate buffer larger than 1024 with (1025 bytes)
console.log(buf.length) // 1024

📦 With prototype

class Example {
  foo: string
  constructor() {
    this.foo = 'bar'
  }

  baz(a: string, b: number) {
    return a + b
  }
}

inject(Example.prototype, 'baz', ({ object, target }, a, b) => {
  console.log('Method baz invoked. Foo property is:', object.foo)
  return target(a, b + 2)
})

const example = new Example()
console.log(example.baz('a', 1))
// Method baz invoked. Foo property is: bar
// a3

ℹ️ Specific usage

If you need to suppress the return value, use noreturn().

⚠️ Use noreturn only when the target function is allowed to return undefined.

let target = (a, b) => a / b

// ❌ Incorrect usage
target = flinject(target, (meta, a, b) => {
  if(b !== 0) return
  console.log(`Divide by zero!`)
  return undefined
})

// ✅ Correct usage
target = flinject(target, ({ noreturn }, a, b) => {
  if(b !== 0) return
  console.log(`Divide by zero!`)
  noreturn()
  // or
  return noreturn()
})