Very simple and easy JavaScript solution!!! Wow (0_o)
\n# Code\n\n/**\n * @param {number[][]} mat\n * @return {number}\n */\nvar diagonalSum = function(mat) {\n    let result = 0;\n    let left = 0, right = mat.len
\n# Code\n```\n/**\n * @param {number[][]} mat\n * @return {number}\n */\nvar diagonalSum = function(mat) {\n    let result = 0;\n    let left = 0, right = mat.length - 1;\n    for(let i = 0; i < mat.length; i++) {\n        if(left == right) {\n            result += mat[i][left] // or mat[i][right]\n        } else {\n            result += mat[i][left]\n            result += mat[i][right]\n        }\n        left++;\n        right--;\n    }\n    return result\n};\n```
['JavaScript']