Both the NASB and the KJV have italics to show extra words added to the text. However, there are thousands of words in both versions that are not italicized in the English, but should be. Modern translations in contemporary English, such as the NIV and The Message, do not have italics, because they are designed to communicate the meaning of scripture, and do not have a focus on being exact. The NRSV is considered more of a study bible, but it does not use italics.

You can do a quick test of your Bible version to see if it tells you when extra words have been added to the text by examining Genesis 1:3. In most translations it says "God said, 'Let there be light,' and there was light." The word there does not exist in Hebrew. (These photos are from the author's copy of the KJV Strongest Strong's Concordance and original working copy of KJV with notations intact.  "NIH" means "Not in Hebrew".)   

The word let is also listed as "Not in Hebrew":

Some scholars argue that the word let is implied in the grammar.  The Ancient Roots Translinear Bible (ARTB) chooses to stick with the Strong's numbering interpretation.

 Because the words aren't there, the ARTB says: God said, 'Light be!' And light was.

The ARTB minimizes extra words as much as possible. Notes have been inserted by the author to help the reader understand the meaning of the text. The author chose to include it in the text rather than a footnote so the reader doesn't miss the significance. For example, in Genesis 29:33, ARTB reads: She conceived again and begot a son, saying, "When Yahweh heard of the hatred to me, he gave me this also, and called his name Simeon (hear)."