JavaScript函数创建名称空间

Question

Below there is the script which create namespace for module, I can't understand how it works after parent = parent[parts[i]] , how does it create nesting? Any suggestions?

var MYAPP = MYAPP || {};
MYAPP.namespace = function (ns_string) {
    var parts = ns_string.split('.'),
        parent = MYAPP,
        i;

    if (parts[0] === "MYAPP") {
        parts = parts.slice(1);
    }
    for (i = 0; i < parts.length; i += 1) {
        // create property if doesn't exist
        if (typeof parent[parts[i]] === "undefined") {
            parent[parts[i]] = {};
        }
        parent = parent[parts[i]];
    }
    return parent;
};

var module2 = MYAPP.namespace('MYAPP.modules.module2');
module2 === MYAPP.modules.module2; // true

Answer 1

Put simply, the function splits the function parameter (a fully qualified name) into its constituent parts (separated by dots). Then, it says, "Does this object exist as a property of the current parent? No, create it as a property of the parent object, and make it the next parent. Yes, set the existing one as the parent object, and repeat for each name." After that, it returns the whole object, which you have assigned to your var module2 .

Answer 2

This is the part you didn't understand:

for (i = 0; i < parts.length; i += 1) {
  // create property if doesn't exist
  if (typeof parent[parts[i]] === "undefined") {
    parent[parts[i]] = {};
  }
  parent = parent[parts[i]];
}


So parent = MYAPP and parts = ['modules', 'module2'];

Here's what's done in the loop:

**i = 0** <br />
typeof parent[parts[0]] equals 'undefined' since MYAPP['modules] doesn't exist <br />
MYAPP['modules'] = {} (MYAPP is parent here and parts[0] equals 'modules') <br />
parent = MYAPP['modules'] <br />
**i = 1** <br />
typeof parent[parts[1]] equals 'undefined' since MYAPP['modules]['module2'] doesn't exist <br />
MYAPP['modules']['module2'] = {} <br />
parent = MYAPP['modules']['module2'] <br />
exists the loop since 1 < 1 is false <br />
returns parent, which is MYAPP['modules']['module2'] <br />