Number of Submatrices That Sum to Target LeetCode solution in JavaScript

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var numSubmatrixSumTarget = function (matrix, target) {
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  let result = 0;
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  for (let i = 0; i < matrix.length; i++) {
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    for (let j = 1; j < matrix[0].length; j++) {
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      matrix[i][j] = matrix[i][j] + matrix[i][j - 1];
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    }
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  }
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  for (let i = 0; i < matrix[0].length; i++) {
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    for (let j = i; j < matrix[0].length; j++) {
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      let dict = {};
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      let cur = 0;
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      dict[0] = 1;
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      for (let k = 0; k < matrix.length; k++) {
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        cur += matrix[k][j] - (i > 0 ? matrix[k][i - 1] : 0);
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        result += dict[cur - target] == undefined ? 0 : dict[cur - target];
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        dict[cur] = (dict[cur] == undefined ? 0 : dict[cur]) + 1;
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      }
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    }
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  }
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  return result;
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};