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JS (.js)

.js file signature | text/javascript

High

Magic Bytes

Offset 0
2F 2A 20 6A 51 75 65 72 79 20

Sources: Apache Tika

All Known Signatures

10 signature variants are documented for .js files across multiple sources.

Hex Signature Offset Sources
2F 2A 20 6A 51 75 65 72 79 20 0 Apache Tika
2F 2A 21 20 6A 51 75 65 72 79 20 0 Apache Tika
2F 2A 21 0 Apache Tika
28 66 75 6E 63 74 69 6F 6E 28 65 2C 75 6E 64 65 66 69 6E 65 64 29 7B 0 Apache Tika
21 66 75 6E 63 74 69 6F 6E 28 77 69 6E 64 6F 77 2C 75 6E 64 65 66 69 6E 65 64 29 7B 0 Apache Tika
2F 2A 20 20 50 72 6F 74 6F 74 79 70 65 20 4A 61 76 61 53 63 72 69 70 74 20 0 Apache Tika
76 61 72 20 50 72 6F 74 6F 74 79 70 65 3D 7B 0 Apache Tika
66 75 6E 63 74 69 6F 6E 20 24 77 28 74 29 7B 0 Apache Tika
2F 2A 2A 20 40 6C 69 63 65 6E 73 65 20 52 65 61 63 74 0 Apache Tika
2F 2A 2A 0 Apache Tika

Extension

.js

MIME Type

text/javascript

Byte Offset

0

Risk Level

High

Validation Code

How to validate .js files in Python

Python 
def is_js(file_path: str) -> bool:
    """Check if file is a valid JS by magic bytes."""
    signature = bytes([0x2F, 0x2A, 0x20, 0x6A, 0x51, 0x75, 0x65, 0x72, 0x79, 0x20])
    with open(file_path, "rb") as f:
        return f.read(10) == signature

How to validate .js files in Node.js

Node.js 
function isJS(buffer: Buffer): boolean {
  const signature = Buffer.from([0x2F, 0x2A, 0x20, 0x6A, 0x51, 0x75, 0x65, 0x72, 0x79, 0x20]);
  return buffer.subarray(0, 10).equals(signature);
}

How to validate .js files in Go

Go 
func IsJS(data []byte) bool {
    signature := []byte{0x2F, 0x2A, 0x20, 0x6A, 0x51, 0x75, 0x65, 0x72, 0x79, 0x20}
    if len(data) < 10 {
        return false
    }
    return bytes.Equal(data[:10], signature)
}

API Endpoint

GET /api/v1/js
curl https://filesignature.org/api/v1/js

See the full API documentation for all endpoints and parameters.

Frequently Asked Questions

What is a .js file?

A .js file is a JS file.

What are the magic bytes for .js files?

The magic bytes for JS files are 2F 2A 20 6A 51 75 65 72 79 20 at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .js file?

To validate a .js file, read the first bytes of the file and compare them against the known magic bytes (2F 2A 20 6A 51 75 65 72 79 20) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .js files?

The primary MIME type for .js files is text/javascript.

Is it safe to open .js files?

JS (.js) files are high risk because they can contain executable code. Never open .js files from untrusted sources. Always scan with antivirus software, verify the source, and consider running in a sandboxed environment.