Dynamically creating keys/values in JavaScript associative array

http://stackoverflow.com/questions/351495/dynamically-creating-keys-in-javascript-associative-array

Somehow all examples, while work well, are overcomplicated:

• They use new Array(), which is an overkill (and an overhead) for a simple associative array (AKA dictionary).
• The better ones use new Object(). Works fine, but why all this extra typing?

This question is tagged "beginner", so let's make it simple.

The uber-simple way to use a dictionary in JavaScript or "Why JavaScript doesn't have a special dictionary object?":

// create an empty associative array (in JavaScript it is called ... Object)var dict = {};   // huh? {} is a shortcut for "new Object()"// add a key named fred with value 42dict.fred = 42;  // we can do that because "fred" is a constant                 // and conforms to id rules// add a key named 2bob2 with value "twins!"dict["2bob2"] = "twins!";  // we use the subscript notation because                           // the key is arbitrary (not id)// add an arbitrary dynamic key with a dynamic valuevar key = ..., // insanely complex calculations for the key    val = ...; // insanely complex calculations for the valuedict[key] = val;// read value of "fred"val = dict.fred;// read value of 2bob2val = dict["2bob2"];// read value of our cool secret keyval = dict[key];

Now let's change values:

// change the value of freddict.fred = "astra";// the assignment creates and/or replaces key-value pairs// change value of 2bob2dict["2bob2"] = [1, 2, 3];  // any legal value can be used// change value of our secret keydict[key] = undefined;// contrary to popular beliefs assigning "undefined" does not remove the key// go over all keys and values in our dictionaryfor(key in dict){  // for-in loop goes over all properties including inherited properties  // let's use only our own properties  if(dict.hasOwnProperty(key)){    console.log("key = " + key + ", value = " + dict[key]);  }}

Deleting values is easy too:

// let's delete freddelete dict.fred;// fred is removed, the rest is still intact// let's delete 2bob2delete dict["2bob2"];// let's delete our secret keydelete dict[key];// now dict is empty// let's replace it, recreating all original datadict = {  fred:    42,  "2bob2": "twins!"  // we can't add the original secret key because it was dynamic,  // we can only add static keys  // ...  // oh well  temp1:   val};// let's rename temp1 into our secret key:if(key != "temp1"){  dict[key] = dict.temp1; // copy the value  delete dict.temp1;      // kill the old key}else{  // do nothing, we are good ;-)}