Create an object out of dot notation

Question

This is a reverse question to this question.

Given an object x={a:1,b:2} and a string c.d=3, modify object x to the following:

Answer 1

Here's a heavily commented version that should be somewhat straightforward to understand.

// stores the configured data
configStore = {};

config = {
  set: function(keyValueString) {

    // Split the string by the =
    var pair = keyValueString.split('=');

    // left of the = is the key path
    var keyPath = pair[0];

    // right of the = is the value to set
    var value = pair[1];

    // split keyPath into an array of keys
    var keys = keyPath.split('.');
    var key; // used in loop

    // the current level of object we are drilling into.
    // Starts as the main root config object.
    var currentObj = configStore;

    // Loop through all keys in the key path, except the last one (note the -1).
    // This creates the object structure implied by the key path.
    // We want to do something different on the last iteration.
    for (var i=0; i < keys.length-1; i++) {

      // Get the current key we are looping
      key = keys[i];

      // If the requested level on the current object doesn't exist,
      // make a blank object.
      if (typeof currentObj[key] === 'undefined') {
        currentObj[key] = {};
      }

      // Set the current object to the next level of the keypath,
      // allowing us to drill in.
      currentObj = currentObj[key];
    }

    // Our loop doesn't handle the last key, because that's when we
    // want to set the actual value. So find the last key in the path.
    var lastKey = keys[keys.length-1]

    // Set the property of the deepest object to the value.
    currentObj[lastKey] = value;
  }
};

// Do it.
config.set('omg.wtf.bbq=123')

// Check it.
alert(configStore.omg.wtf.bbq); // 123