answering questions in chrome.md

Author: TzeMingHo

Sprint-1/4-stretch-explore/chrome.md

@@ -11,8 +11,13 @@ In the Chrome console,
 invoke the function `alert` with an input string of `"Hello world!"`;
 
 What effect does calling the `alert` function have?
+The alert function call a small separate window pop out, written "Hello world!". There is a OK button at the bottom right to dismiss it.
 
 Now try invoking the function `prompt` with a string input of `"What is your name?"` - store the return value of your call to `prompt` in an variable called `myName`.
 
 What effect does calling the `prompt` function have?
+The prompt function pop out a small window similar to alert but it has a input section where I can type my name.
+
 What is the return value of `prompt`?
+The return value of prompt is a string. If we did not enter anything and pressed ok, the value is also a string.
+However, if we pressed cancel, it will return null.