Question

I’m creating a dictionary object in javascript (eg associate array)

var myobj = {
  "a" : "Some string",
  "b" : "Some string else"
}

if I access myobj.a, it will return “Some string”
but if I access something not in the list myobj.c it return undefined.
Is there any way to set object getter to return something like: “Key not available”
Can we use prototype…
Thanks for any help

Answer 1

Yes/No.

No

There is no way to intercept generic get’s on keys using ES5

Yes

Use methods

var Dictionary = {
    get: function (key) {
        if ({}.hasOwnProperty.call(this, key)) {
            return this[key]
        }
        return "Key not available"
    }
}

Note there are some pitfalls using objects as dictionary, consider using a module like strmap

Use ES6 proxies (not implemented in browsers)

Using an ES6 proxy

var dictionary = Proxy({}, {
    get: function (target, name) {
        if ({}.hasOwnProperty.call(target, name)) {
            return target[name
        }
        return "Key not available"
    }
})

Using an ES6 Map (shimmable)

Just use an ES6 map

var dict = new Map
dict.set("foo", "bar")
dict.get("foo")