Building object hierarchy from a 'namespace

问题:

I'm trying to write a function that takes a string representing a namespace (e.g. "MyCompany.UI.LoginPage") and defines each segment of the namespace as an object if it doesn't already exist. For example, if "MyCompany.UI.LoginPage" wasn't an object, it would evaluate this:

MyCompany = {};
MyCompany.UI = {};
MyCompany.UI.LoginPage = {};

I would like to do this by enumerating each character of the "namespace" (string) argument and defining each object as the enumeration reaches period characters.

How can I enumerate the characters of a string in JavaScript?

回答1:

You can access the characters of a string directly by its index, using the String.prototype.charAt method:

var str = "foo";
for (var i = 0; i < str.length; i++) {
  alert(str.charAt(i));
}

But I don't think that you want to traverse your namespace string character by character, you can use the String.prototype.split method, to get an array containing the namespace levels using the dot (.) character as a separator, e.g.:

var levels = "MyCompany.UI.LoginPage".split('.');
// levels is an array: ["MyCompany", "UI", "LoginPage"]

But I think your question goes further to this, and I will give you a more advanced starting point, I made a recursive function that will allow you to do exactly what you want, initialize several nested object levels using a string:

Usage:

initializeNS('MyCompany.UI.LoginPage');
// that will create a MyCompany global object

// you can use it on an object to avoid globals also
var topLevel = {};
initializeNS('Foo.Bar.Baz', topLevel);

// or
var One = initializeNS('Two.Three.Four', {});

Implementation:

function initializeNS(ns, obj) {
  var global = (function () { return this;})(), // reference to the global object
      levels = ns.split('.'), first = levels.shift();
  obj = obj || global; //if no object argument supplied declare a global property
  obj[first] = obj[first] || {}; // initialize the "level"
  if (levels.length) { // recursion condition
    initializeNS(levels.join('.'), obj[first]);
  }
  return obj[first]; // return a reference to the top level object
}

You will have to improve this function, for example you will need to sanitize the string...

回答2:

Convert the string into an array of characters with this code:

var $letterArray = [];

for (var $i = 1; $i <= $yourString.length; $i++)
{
    $letterArray[$i] = $yourStringtring.substring(($i - 1), $i);
}

Then you can enumerate over each character in the string array $letterArrary