decode-minified-js-gates

Decode Minified JS Gates

Read the call-site context around a flag string in a minified JavaScript bundle and produce a gate-mechanics record: which reader variant, what default, what conjunction, what role. Where probe-feature-flag-state answers "is this gate on or off?", this skill answers the prerequisite question — "what does this gate actually do?"

When to Use

• A flag surfaced by sweep-flag-namespace cannot be classified from its name alone.
• The binary uses more than one gate-reader function and you need to know which one a flag invokes.
• A gate's "default" appears non-boolean ({}, null, a numeric literal) and you need to decode the actual reader variant.
• You suspect a kill-switch (inverted gate) but cannot confirm from the flag name.
• A predicate combines multiple gates with && and you need to enumerate the co-gates before probing any of them.

Inputs

• Required: a minified JavaScript bundle file (.js, .mjs, .bun).
• Required: a target flag string to decode, in literal form.
• Optional: a list of known reader function names from a prior decode pass — speeds Step 2.
• Optional: a context-window size override; default is 300 chars before, 200 chars after the flag occurrence.

Procedure

Step 1: Extract the Context Window

Locate the flag string and capture an asymmetric window around each occurrence. The pre-context (before the flag) is where the reader function name lives; the post-context (after) is where the default value and conjunction live.

BUNDLE=/path/to/cli/bundle.js
FLAG=acme_widget_v3                   # synthetic placeholder
PRE=300
POST=200

# All byte offsets where the flag string occurs
grep -boE "\"${FLAG}\"" "$BUNDLE" | cut -d: -f1 > /tmp/decode-offsets.txt
wc -l /tmp/decode-offsets.txt

# Capture an asymmetric window per occurrence
while read -r offset; do
  start=$((offset - PRE))
  [ "$start" -lt 0 ] && start=0
  length=$((PRE + POST))
  echo "=== offset $offset ==="
  dd if="$BUNDLE" bs=1 skip="$start" count="$length" 2>/dev/null
  echo
done < /tmp/decode-offsets.txt > /tmp/decode-windows.txt

less /tmp/decode-windows.txt