JS alternative of Ruby’s method_missing

Why? Because!

Jul 4, 2017
1 min read
#guides
#javascript
#metaprogramming

Warning

This post was written more than 5 years ago, and its contents may be out of date

Some guy in telegram JS chat asked how to do something like this:

let types = new Types()

console.log(types.AnythingYouCouldImagine({ a: "some data" }))
// => { type: "AnythingYouCouldImagine", data: { a: "some data" } }

In ruby we can use handy `method_missing“ callback, but in js we don’t have anything that can turn any class into this. But in js we have thing called proxy.

This will work like “catchall”:

let proxy = new Proxy({}, {
  get(target, prop) {
    return (data) => {
      return {
        type: prop,
        data: data
      }
    }
  }
})

console.log(proxy.Anything('data')) // { type: "Anything", data: "data" }

And this one will work like method_missing:

class A {
  alreadyDefined(arg) {
    return { a: "Wow!", arg: arg }
  }
}

let proxy = new Proxy(new A(), {
  get(target, prop) {
    if(target[prop]) return target[prop]

    return (data) => {
      return {
        type: prop,
        data: data
      }
    }
  }
})

console.log(proxy.alreadyDefined('data'))
// { a: "Wow!", arg: "data "}
console.log(proxy.Anything('data'))
// { type: "Anything", data: "data" }

Licensed under CC BY-NC 4.0

JS alternative of Ruby’s method_missing

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