Dynamically create Javascript Object

Question

Given a strings like 'param1.param2.param3' and a value that should be set on the last parameter, is there a better way than the following to dynamically create an Object and reuse the function to create more parameters on the Object, some which may share a parent parameter? This function also assumes every parameter on the parent Object is an Object with parameters. The purpose is to construct a JSON Object dynamically for a PUT/PATCH request.

function(o,prop,val) {
            prop = prop.split('.');
            prop.forEach(function(property,i){
                if(i===0 && typeof(o[property]) === 'undefined'){
                    o[property] = {};
                    if(prop.length === 2){
                        o[prop[0]][prop[1]] = val;
                    }
                }
                else if(i===1 && typeof(o[prop[0]][property]) === 'undefined'){
                    o[prop[0]][property] = {};
                    if(prop.length === 3){
                        o[prop[0]][prop[1]][prop[2]] = val;
                    }
                } else if(i===1 && typeof(o[prop[0]][property]) === 'object'){
                    if(prop.length === 3){
                        o[prop[0]][prop[1]][prop[2]] = val;
                    }
                }
                else if(i===2 && typeof(o[prop[0]][prop[1]][property]) === 'undefined'){
                    o[prop[0]][prop[1]][property] = {};
                    if(prop.length === 4){
                        o[prop[0]][prop[1]][prop[2]][prop[3]] = val;
                    }
                } else if(i===2 && typeof(o[prop[0]][prop[1]][property]) === 'object'){
                    if(prop.length === 4){
                        o[prop[0]][prop[1]][prop[2]][prop[3]] = val;
                    }
                }
            });
            return o;
        };

Here is a Fiddle https://jsfiddle.net/cn25o1vf/

Answer 1

It seems odd to special-case the string "object" when preparing an object for serialization, so I came up with the following code:

var createObjectFromParam = function (o, prop, val) {
    var parts = prop.split('.');
    var last = o;
    while (parts.length) {
        var part = parts.shift();
        if (parts.length > 0) {
            last[part] = last[part] || {};
            last = last[part];
        } else {
            last[part] = val; // Add conditional expressions here
        }
    }
    return last;
}

The code does the following:

• Creates a temporary variable (last) to contain the current "level" of the object hierarchy.
• Loops through the array. Note that while (parts.length) will stop the loop when there are no longer parts in the array.
• Take the next part of the prop. shift pulls the first element of the array out.
• If we're not at the last element
  • If the element with the specified name exists at the level, use that
  • If not, create an object at that level
• Otherwise, add a property with the specified value to the object.
• Finally, return the created object.

Given the example in the jsFiddle (updated here), this would produce the following structure:

{
    "ready": {
        "set": "go"
    },
    "another": "object",
    "happy": {
        "happy": {
            "joy": "joy",
            "foo": "bar",
            "happy": "happy"
        }
    }
}

To keep that original special-casing, just replace the commented line with something like:

last[part] = val === 'object' ? {} : val === 'undefined' ? : undefined : val;