Design Authentication Manager LeetCode solution in JavaScript

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// O(n)
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var AuthenticationManager = function (timeToLive) {
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  this.ttl = timeToLive;
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  this.map = {};
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};
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AuthenticationManager.prototype.generate = function (tokenId, currentTime) {
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  this.map[tokenId] = currentTime + this.ttl;
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};
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AuthenticationManager.prototype.renew = function (tokenId, currentTime) {
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  let curr = this.map[tokenId];
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  if (curr > currentTime) {
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    this.generate(tokenId, currentTime);
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  }
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};
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AuthenticationManager.prototype.countUnexpiredTokens = function (currentTime) {
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  return Object.keys(this.map).filter((key) => this.map[key] > currentTime)
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    .length;
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};