All O`one Data Structure LeetCode solution in JavaScript

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var AllOne = function () {
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  this.map = new Map();
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  this.pre = "";
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};
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/**
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 * @param {set} map
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 * @param {function} handler
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 * @return {map}
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 */
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AllOne.prototype.sort = function (map, handler) {
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  return new Map([...map].sort(handler));
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};
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/**
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 * @param {string} key
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 * @return {void}
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 */
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AllOne.prototype.inc = function (key) {
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  this.map.set(key, this.map.get(key) + 1 || 1);
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  this.pre = "inc";
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};
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/**
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 * @param {string} key
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 * @return {void}
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 */
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AllOne.prototype.dec = function (key) {
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  this.map.get(key) == 1
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    ? this.map.delete(key)
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    : this.map.set(key, this.map.get(key) - 1);
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  this.pre = "dec";
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};
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/**
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 * @return {string}
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 */
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AllOne.prototype.getMaxKey = function () {
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  if (this.pre != "max") {
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    this.map = this.sort(this.map, (a, b) => b[1] - a[1]);
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  }
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  this.pre = "max";
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  return this.map.keys().next().value || "";
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};
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/**
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 * @return {string}
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 */
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AllOne.prototype.getMinKey = function () {
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  if (this.pre != "min") {
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    this.map = this.sort(this.map, (a, b) => a[1] - b[1]);
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  }
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  this.pre = "min";
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  return this.map.keys().next().value || "";
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};