Input is rejected
remove surrounding quotes, confirm the Standard/URL-safe setting, check padding and verify that the value was not truncated.
Convert Base64 to JavaScript
Decode Base64 to JavaScript, review the restored output and copy or download it. Use the standard or URL-safe option required by the source.
Base64 utility · Fast, exact Base64 conversion
What this tool does
Paste the Base64 value and decode it to JavaScript. The tool returns the corresponding byte or text representation; it does not automatically validate, reformat or execute the result.
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Paste text or choose a file
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Choose an action
Encode, decode or inspect
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Review output and byte details
1. Input
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2. Action
3. Output
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4. Quick actions
5. Base64 information
DescriptionBase64 represents bytes as text; it is not encryption.
AlphabetA-Z, a-z, 0-9, +, /, =
Input size0 characters / 0 bytes
Output size0 characters / 0 bytes
PaddingUses = to complete a four-character group.
StatusReady
How it works
Input bytes
101010 111100 110101 ...
Split into 6-bit groups
101010 111100 110101 ...
Convert to indexes
42 60 53 ...
Base64 characters
q 8 1 ...
How to convert Base64 to JavaScript
Paste the Base64 string you want to decode.
Keep Decode selected and choose Standard or URL-safe Base64 when the control is available.
Review the output and byte information, then copy or download the result.
Output and format behavior
The converter returns JavaScript source as text without evaluating it. Treat untrusted code as plain text and review it before running it anywhere.
Use Standard Base64 for the normal RFC 4648 alphabet. Use URL-safe only when the receiving system expects Base64URL; padding rules can differ by protocol.
Expert tip
Treat decoded source as untrusted text. Review first, then run it only in an isolated environment appropriate to the language.
When this is useful
Typical workflows include:
- Return encoded source to readable text for audit, code review or troubleshooting.
- Inspect or compare a small payload when the original representation is opaque or difficult to paste safely.
- Create a reproducible test fixture without manually rewriting the source bytes.
Limitations and safety
Important constraints:
- Base64 normally adds about one third to the byte payload, before any data-URL prefix or surrounding markup.
- Base64 is reversible encoding, not encryption. Anyone who receives the string can decode the original bytes.
- The converter returns source as text only; it does not render, evaluate, sanitize, minify or execute the supplied code.
Troubleshooting
Decoded source looks suspicious
do not render or execute it. Review as plain text and use appropriate security tooling outside this converter.
Frequently asked questions
What exactly is preserved?
The converter returns JavaScript source as text without evaluating it. Treat untrusted code as plain text and review it before running it anywhere.
Does decoding or encoding run the source code?
The converter returns source as text and does not execute it. Code can run only after another system loads, renders or evaluates the result.
What is the difference between standard Base64 and Base64URL?
Standard Base64 uses + and /. Base64URL uses - and _ and may omit padding; choose the form required by the receiving system.
Why is my Base64 input rejected?
Check for unsupported characters, a Standard/Base64URL mismatch, damaged padding or a truncated value. Also remove surrounding quotes that are not part of the payload.
Related Base64 tools
Continue with the localized page that matches the next operation:
Paste your input above, run the conversion, and copy or download the result.