Project Euler problems (numbering) : follow naming convention.

Project-Euler/Problem004.js

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+// https://projecteuler.net/problem=4
+/* A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
+   Find the largest palindrome made from the product of two 3-digit numbers.
+*/
+export const largestPalindromic = (digits) => {
+  let i
+  let n
+  let m
+  let d
+  let limit
+  let number = 0
+
+  for (i = 1; i < digits; i++) {
+    number = 10 * number + 9
+  }
+  const inf = number // highest (digits - 1) number, in this example highest 2 digit number
+  const sup = 10 * number + 9 // highest (digits) number, in this example highest 3 digit number
+
+  const isPalindromic = (n) => {
+    let p = 0
+    const q = n
+    let r
+    while (n > 0) {
+      r = n % 10
+      p = 10 * p + r
+      n = Math.floor(n / 10)
+    }
+    return p === q // returning whether the number is palindromic or not
+  }
+
+  for (n = sup * sup, m = inf * inf; n > m; n--) {
+    if (isPalindromic(n)) {
+      limit = Math.ceil(Math.sqrt(n))
+      d = sup
+      while (d >= limit) {
+        if (n % d === 0 && n / d > inf) {
+          return n
+        }
+        d -= 1
+      }
+    }
+  }
+  return NaN // returning not a number, if any such case arise
+}