Deep proxy implementation for TypeScript
npm install @qiwi/deep-proxy
shell script
npm
npm i @qiwi/deep-proxyyarn
yarn add @qiwi/deep-proxy
`Key features
* Single proxy handler with rich context instead of verbose traps mapping
* Proxy self-reference in handler context (meaningful for methods binding)
* JS, TS and Flow support
* Magic directives:
* to build an infinite nested proxy chain
* DEFAULT to switch to the object's default behavior
* Caching
* Trap params parsingUsage
`typescript
import {DeepProxy} from '@qiwi/deep-proxy'const target = {foo: 'bar', a: {b: 'c'}}
const proxy = new DeepProxy(target, ({trapName, value, key, DEFAULT, PROXY}: THandlerContext) => {
if (trapName === 'set') {
throw new TypeError('target is immutable')
}
if (trapName === 'get') {
if (typeof value === 'object' && value !== null) {
return PROXY
}
if (key === 'd') {
return 'baz'
}
return 'qux'
}
return DEFAULT
})
proxy.foo // qux
proxy.a.b // qux
proxy.bar // qux
proxy.d // baz
proxy.a = 'a' // TypeError
`
FP adepts may use factory instead of DeepProxy class and get some magic.
`ts
import {createDeepProxy} from '@qiwi/deep-proxy'// Regular usage case
const handler = ({DEFAULT}) => DEFAULT
const proxy1 = createDeepProxy(target, handler)
// Passing defaults through this context
const customProxyFactory = createDeepProxy.bind({handler})
const proxy2 = customProxyFactory(target)
`All the traps follow to the single handler, so you're able to build various complex conditions in one place. This approach might be useful if you need some kind of "rich" model, but you don't want to complicate DTO.
typescript
if (path.length > 10) {
if (prop === 'foo' || ['get', 'set', 'ownKeys'].includes(trapName)) {
return DEFAULT
} throw new Error('Bla-bla')
}
if (trapName === 'set' && typeof value !== 'number') {
throw new TypeError('only
number type is allowed')
}// and so on
return DEFAULT
`Another example. Imagine a client which uses an unstable channel with 10% of loss.
typescript
const client = createClient({...opts})
await client.foo(...args) // 90% of successconst clientWithRetry = new DeepProxy(client, ({value, trapName}: THandlerContext) => {
if (trapName === 'get') {
if (typeof value === 'function') {
return retryify(value, 2)
}
if (typeof value === 'object' && value !== null) {
return PROXY
}
}
return DEFAULT
})
await clientWithRetry.foo(...args) // 99% of success
`
Metrics, debugging, throttling — all becomes better with the deep proxy.Traps
https://262.ecma-international.org/12.0/#table-proxy-handler-methods
js
'defineProperty',
'deleteProperty',
'apply',
'construct',
'get',
'getOwnPropertyDescriptor',
'getPrototypeOf',
'has',
'isExtensible',
'ownKeys',
'preventExtensions',
'set',
'setPrototypeOf'
`Directives
| Directive | Description |
|-----------|------------------------------------------------------------------------------------------------------------------|
| | Returns standard flow control. The current operation (get, set, ownKeys, etc) will be performed as without proxy.|
| PROXY | Returns a proxy of nested object with parent's proxy handler. |A bit more sugar on top: by default
PROXY directive uses value from context, but you can pass your own.
`typescript
const proxy = new DeepProxy({foo: {bar: 'baz'}}, ({value, trapName}) => {
if (trapName === 'get' && typeof value === 'object' && value !== null) {
return PROXY({baz: 'qux'})
} return DEFAULT
})
proxy.foo.baz // 'qux'
`THandlerContext
ts
type THandlerContext = {
target: T // proxy target object/function parameters: any[] // trap arguments as is: [target, , , *]
name: keyof T, // property name
val: any, // property value
receiver: any, // receiver ('get' or 'set' traps)
args: any[], // arguments array ('apply' trap)
descriptor: PropertyDescriptor, // property descriptor ('defineProperty', 'deleteProperty' trap)
thisValue: any, // this context of 'apply' trap
prototype: any, // prototype of 'setPrototypeOf' trap
trapName: TTrapName // proxy handler trap: get, set, ownKeys and so on
traps: TTraps // proxy handler map reference
root: TTarget // root level proxy's target
path: string[] // path to current proxy from root
key?: keyof T // prop key if defined in trap args
value: any // current field value by key
newValue?: any // new assigned value (#set())
handler: TProxyHandler // handler reference
PROXY: symbol // directives
DEFAULT: symbol
proxy: TTarget // proxy reference
}
`Caching
factory returns the stored proxy reference if the arguments match to any previous call:
1) target refs are strictly equal
2) root refs equal too
3) path values matchNote, this is not a regular memoization, but a loosely coupled
WeakMap, so unused proxies can be cleaned up by GC.
`typescript
export type TProxyCache = {
// root object refers to some targets objects,
// that refer to map, that binds nested paths with their traps
traps: WeakMap>> // And these traps refer to proxies
proxies: WeakMap>
}
``