Add many objects to a collection in a JavaScript object
Before I answer your question, I want to clean some things up first.




this[listField]={
    'formField':formField,
    'fieldType':fieldType
}



Whoa. You are creating an entire new property here based on input a caller gave you. Then, you are setting this to a uniformly designed object every time.


Not good practice
We can OOP this up.


Every time this method is called, an object is created with a certain "shape" (certain properties, etc.)

For that, we create a new class:

function ListField(name, formField, fieldType) {
    ... fill in the rest with property setting ...
}


Now our data is more easily help together.



Time to fix the bad practice mentioned above.

Instead of modifying the very structure of the parent object every time add is called, you should instead push the new ListField object into an array.

This will keep all the added ListField objects in one, easy to access place. This all removes all bad practices.




  Is there a more efficient way to do this?


Sure.

Considering you know that you are going to be sending in a large amount of ListFields, then why not let add take an array?

FieldMap.prototype.add = function(arr) { // use better name
    for(var i = 0; i &lt; arr.length; i++) {
        this.listFields.push(arr[i]);
    }
}


Then, to call, just pass in an array of the various FieldMaps.

No, this will not making typing more easily (well, it will by a little bit). However, since the data you are providing is arbitrary, then there is no way you can do this with patterns and loops.

However, this will speed up your code. Instead of calling a method 20+ times in a row, you are calling this method a single time and this method is using a loop 20+ times; a much more efficient task.