How do I Compare 2 sentences and get index of the different words

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Javascript

jQuery

, +

I have a contenteditable div

<div id="editableDiv" contenteditable="true">
    hey @twitter is #awesome
</div>

I will collect its html content as $('#editableDiv').html()

html content collected at this time (1): <b>hey</b> <span style="color:blue">@twitter</span> #awesome


html content collected after some time (2): <b>hey</b> <span style="color:blue">@twitter</span> #awesome #website

And now, would like to calculate the differences between (1) and (2) and get the index of different words.
As per this, website is the only word different in (1) and (2) and so
its starting index and ending index must be something like (61, 69)