Design a Number Container System LeetCode solution in JavaScript

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var NumberContainers = function () {
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  this.obj = {};
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  this.global = {};
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};
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NumberContainers.prototype.change = function (index, number) {
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  if (this.global[index]) {
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    for (var key in this.obj) {
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      let ind = this.obj[key].indexOf(index);
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      if (ind != -1) {
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        this.obj[key].splice(ind, 1);
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        if (this.obj[number]) this.obj[number].push(index);
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        else this.obj[number] = [index];
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        this.global[index] = 1;
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        return;
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      }
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    }
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  }
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  if (this.obj[number]) this.obj[number].push(index);
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  else this.obj[number] = [index];
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  this.global[index] = 1;
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};
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NumberContainers.prototype.find = function (number) {
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  if (this.obj[number]) {
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    if (this.obj[number].length == 0) return -1;
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    else return Math.min(...this.obj[number]);
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  }
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  return -1;
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};