Count Number of Texts LeetCode solution in JavaScript

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var countTexts = function (pressedKeys) {
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  const MOD = 1e9 + 7;
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  const n = pressedKeys.length;
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  const dp = new Array(n + 1).fill(0);
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  dp[0] = 1;
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  let lastChar = "";
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  let repeatCount = 0;
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  for (let i = 1; i <= n; ++i) {
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    const currChar = pressedKeys[i - 1];
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    if (currChar != lastChar) repeatCount = 0;
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    lastChar = currChar;
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    repeatCount += 1;
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    dp[i] = (dp[i] + dp[i - 1]) % MOD;
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    if (i >= 2 && repeatCount >= 2) dp[i] = (dp[i] + dp[i - 2]) % MOD;
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    if (i >= 3 && repeatCount >= 3) dp[i] = (dp[i] + dp[i - 3]) % MOD;
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    if ((currChar == "7" || currChar == "9") && i >= 4 && repeatCount >= 4)
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      dp[i] = (dp[i] + dp[i - 4]) % MOD;
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  }
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  return dp[n];
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};