Decode Ways II LeetCode solution in JavaScript

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var numDecodings = function (s) {
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  let len = s.length;
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  if (len === 0) return s;
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  let mod = Math.pow(10, 9) + 7;
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  let dp = new Array(len + 1).fill(0);
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  dp[0] = 1;
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  if (s[0] == 0) dp[1] = 0;
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  else if (s[0] == "*") dp[1] = 9;
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  else dp[1] = 1;
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  for (let i = 2; i <= len; i++) {
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    if (s[i - 1] == "*") {
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      dp[i] += 9 * dp[i - 1];
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    } else if (s[i - 1] != 0 && s[i - 1] != "*") {
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      dp[i] += dp[i - 1];
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    }
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    if (s[i - 2] == 1) {
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      if (s[i - 1] == "*") dp[i] += 9 * dp[i - 2];
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      else dp[i] += dp[i - 2];
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    } else if (s[i - 2] == 2) {
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      if (s[i - 1] < 7) dp[i] += dp[i - 2];
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      else if (s[i - 1] == "*") dp[i] += 6 * dp[i - 2];
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    } else if (s[i - 2] == "*") {
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      if (s[i - 1] == "*") dp[i] += 15 * dp[i - 2];
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      else if (s[i - 1] >= 0 && s[i - 1] <= 6) dp[i] += 2 * dp[i - 2];
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      else if (s[i - 1] >= 7) dp[i] += dp[i - 2];
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    }
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    dp[i] = dp[i] % mod;
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  }
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  return dp[len] % mod;
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};