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A simple command example

175

The 

changeCase()

 function first tests the property 

document.forms[0].elements[0].checked

. The 

document.forms[0].elements[0]

 

property refers to the first element in the first form of the current document object, which is 
the UI for the extension. The 

checked

 property has the value 

true

 if the element is checked 

(or enabled) and 

false

 if it is not. In the interface, 

elements[0]

 refers to the first radio 

button, which is the Uppercase button. Because one of the radio buttons is always checked 
when the user clicks OK, the code assumes that if the choice is not uppercase, it must be 
lowercase. The function sets the variable 

uorl

 to "u" or "l" to store the user’s response. 

The remaining code in the function retrieves the selected text, converts it to the specified case, 
and copies it back in place in the document.

To retrieve the selected text for the user’s document, the function gets the DOM. It then gets 
the root element of the document, which is the 

html

 tag. Finally, it extracts the whole 

document into the 

theWholeDoc

 variable.

Next, 

changeCase()

 calls 

getSelectedNode()

 to retrieve the node that contains the selected 

text. It also retrieves any child nodes (

theSelNode.childNodes)

 in case the selection is a tag 

that contains text, such as 

<b>text</b>

.

If there are child nodes (

hasChildNodes()

 returns the value 

true

), the command loops 

through the children looking for a text node. If one is found, the text 
(

theChildren[i].data

) is stored in 

selText

, and the offsets of the text node are stored in 

theSel

.

If there are no child nodes, the command calls 

getSelection()

 and stores the beginning and 

ending offsets of the selection in 

theSel

. It then extracts the string between those two offsets 

and stores it in 

selText

.

The function then checks the 

uorl

 variable to determine whether the user selected uppercase. 

If so, the function writes the HTML code back to the document in sections: first, the 
beginning of the document to the beginning of the selection; then the selected text, 
converting it to uppercase (

selText.toUppercase()

); and last, the end of the selected text to 

the end of the document.

If the user selects lowercase, the function performs the same operation, but calls 

selText.toLowerCase()

 to convert the selected text to lowercase.

Finally, 

changeCase()

 resets the selection and calls 

window.close()

 to close the UI.