Question

I have a simple function constructor and want to assign a DOM element ID to one of the properties. When this is done outside of a constructor you have to put the ID in quotation marks IE getElementById(” whatever “);

In my constructor I am not sure if I need to do this, how do add them, nor if I am formatting this correctly.

<form id="form">
<input type="text" id="bookText" value="Book">
</form>

<script>

function Item(itemName,itemDomID){
this.itemName = document.getElementById(this.itemDomID);   
};

var mybook = new Item(book,bookText);       // new object.


</script>

Answer 1

I have a simple function constructor and want to assign a DOM element
ID to one of the properties. When this is done outside of a
constructor you have to put the ID in quotation marks IE
getElementById(” whatever “);

An element ID is a string, assigning a string to an object property does not require a function, just an assignment:

mybook.book = 'bookText';

When passing values using variables, just use the variable name. The expression will be evaluated to return the value. The constructor should be (note changes to original):

function Item(itemName, itemDomID){

    this[itemName] = document.getElementById(itemDomID);   

}

Note the use of square brackets to assign the value of itemName to the new property name, rather than the literal string “itemName”.

So when calling the constructor, string values can be passed:

var mybook = new Item('book', 'bookText');

The values will be assigned to the variables in the function in order, so itemName is assigned the value “book” and itemDomID is assigned the value “bookText”.

Inside the constructor, the new object will be given a property named “book” with a value of whatever is returned by document.getElementById('bookText'), which will either be a reference to an element, or null if no element with that ID is found.