Find the Middle Index in Array LeetCode solution in JavaScript

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var findMiddleIndex = function (nums) {
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  for (let i = 0; i < nums.length; i++) {
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    let leftNums = nums.slice(0, i).reduce((a, b) => a + b, 0);
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    let rightNums = nums.slice(i + 1).reduce((a, b) => a + b, 0);
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    if (leftNums === rightNums) {
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      return i;
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    }
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  }
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  return -1;
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};