How to use a delimited string to locate and modify an object key at an arbitrary depth?

Question

This is problem-solving q; nothing's gone wrong, I'm just stumped about how to advance. Basically I want my users to be able to

1. Point to an arbitrary key of an object with arbitrary depth via a string representation of the "path";
2. Confirm that each step of the "path" exists; and
3. Implement CRUD-like functionality

I can verify that each key is valid, but I'm just stumped on how to then utilize said path without ultimately using an eval() statement, but of course I needn't explain why I'm not going to let a call to eval() get anywhere near arbitrary user input. Here's as far as I can get:

const SEP = "/" //in reality this is set by the server,
MyObjInterface = function() {
    this.params = {};
    this.response = {};

    // suppose some initialization business, then on to the question... ( >.>)

    this.updateOb= function(path, value ) {
        path = path.replace('\\' + DS,"$DIRECTORY_SEPARATOR").split(DS);

        for (var i = 0; i < path.length; i++) {
            path[i].replace("$DIRECTORY_SEPARATOR",DS);
        }

        if (typeof(path) != "object" || path.length < 3) { // 3 = minimum depth to reach a valid field in any rset scheme
            throw "Could not create rset representation: path either incorrectly formatted or incomplete."
        }

        var invalidPath = false;
        var searchContext = path[0] === "params" ? this.params : this.response;
        for (var i = 1; i < path.length - 1; i++) {
            if (invalidPath) { throw "No key found in rset at provided path: [" + path[i] + "]."; }

            if (i === path.length - 1) {
                searchContext[path[1]] = value;
                return true;
            }
            if (path[i] in searchContext) {
                searchContext = searchContext[path[i]];
            } else {
                invalidPath = true;
            }

        }
    }
};

Answer 1

You break the path up in to components, then you recursively walk the tree.

My JS is weak, so I'll pseudo code.

path = "go.down.three";
listOfElements = breakUpPath(path); // Now listOfElement = ["go", "down", "three"];
myObj = setObjectValue(myObj, listOfElement, "I'm a value");

function setObjectValue(obj, listOfElements, value) {
    var firstPart = pop(listOfElements); // get and remove top of listOfElements stack
    if (length(listOfElements) == 0) { // last element of the path, set the value
        obj[firstPart] = value;
        return obj;
    } else {
        // check if a property exists at all
        var firstValue = obj[firstPart];
        if (firstValue == null) {
            firstValue = new Object();
            obj[firstPart] = firstValue;
        }
        obj[firstPart] = setObjectValue(firstValue, listOfElement, value);
    }
}

So, my as I said, my JS is weak (really weak, I can't really even spell JavaScript). Needless to say, this is untested.

But something like that is what you're looking for. Just work your way down the elements of the path.