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Determine if string is in base64 using JavaScript

Asked 2011-10-22T14:55:22.397
67

I'm using the window.atob('string') function to decode a string from base64 to a string. Now I wonder, is there any way to check that 'string' is actually valid base64? I would like to be notified if the string is not base64 so I can perform a different action.

javascript base64
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27

I would use a regular expression for that. Try this one:

/^([0-9a-zA-Z+/]{4})*(([0-9a-zA-Z+/]{2}==)|([0-9a-zA-Z+/]{3}=))?$/

Explanation:

^                          # Start of input
([0-9a-zA-Z+/]{4})*        # Groups of 4 valid characters decode
                           # to 24 bits of data for each group
(                          # Either ending with:
    ([0-9a-zA-Z+/]{2}==)   # two valid characters followed by ==
    |                      # , or
    ([0-9a-zA-Z+/]{3}=)    # three valid characters followed by =
)?                         # , or nothing
$                          # End of input
answered 2011-10-24T10:20:06.157

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