Question

I want need to translate a notation (e.g. ‘main:message:new’) to the referred object property (resource[main][message][new]).

var notation = 'main:message:new';

var ressource = {
    message: { new: 'something' }
};

var splitKeys = function(keys, object) {
    var keys, pointer;
    pointer = object;
    keys = keys.split(':');
    for (i = 0; i < keys.length; i++) {
        // here is the error
        if (pointer[keys[i]] === undefined) break;
        pointer = pointer[keys[i]];
    }
    return pointer;
};

console.log(splitKeys(notation, ressource));

As you see I got problems with the error handling. If there is a ressource notation which doesn’t match a concrete ressource I want to return nothing. Unfortunately I always get an error thrown ‘cannot read property undefined of undefined’…

Answer 1

The first property name, called main, is not present in your resource object, thus your method will always return the entire object instead of the property value you are aiming at, which is { new: 'something' }:

var splitKeys = function(keys, object) {
    var pointer = object;
    var parent = pointer;
    keys = keys.split(':').slice(1); // exclude `main`
    for (var i = 0; i < keys.length; i++) {
        if (pointer[keys[i]] === undefined) break;
        parent = pointer;
        pointer = pointer[keys[i]];
    }
    return parent;
};

This will return the new object, i.e., { new: 'something' }. If you want to return the property value instead, return pointer instead of parent.

DEMO.