Getting the dimensions of a multidimensional JS array.

matrix-dimension.js

// Assumes a valid matrix and returns its dimension array.
// Won't work for irregular matrices, but is cheap.
function dim(mat) {
    if (mat instanceof Array) {
        return [mat.length].concat(dim(mat[0]));
    } else {
        return [];
    }
}

// Makes a validator function for a given matrix structure d.
function validator(d) {
    return function (mat) {
        if (mat instanceof Array) {
            return d.length > 0
                && d[0] === mat.length
                && every(mat, validator(d.slice(1)));
        } else {
            return d.length === 0;
        }
    };
}

// Combines dim and validator to get the required function.
function getdim(mat) {
    var d = dim(mat);
    return validator(d)(mat) ? d : false;
}

// Checks whether predicate applies to every element of array arr.
// This ought to be built into JS some day!
function every(arr, predicate) {
    var i, N;
    for (i = 0, N = arr.length; i < N; ++i) {
        if (!predicate(arr[i])) {
            return false;
        }
    }

    return true;
}

// Test code from Stackoverflow answer
// http://stackoverflow.com/questions/13814621/how-can-i-get-the-dimensions-of-a-multidimensional-javascript-array/13832026#13832026

console.log(getdim(123)); // []
console.log(getdim([1])); // [1]
console.log(getdim([1, 2])); // [2]
console.log(getdim([1, [2]])); // false
console.log(getdim([[1, 2], [3]])); // false
console.log(getdim([[1, 2],[1, 2]])); // [2, 2]
console.log(getdim([[1, 2],[1, 2],[1, 2]])); // [3, 2]

console.log(getdim([[[1, 2, 3],[1, 2, 4]],[[2, 1, 3],[4, 4, 6]]])); // [2, 2, 3]

console.log(getdim([[[1, 2, 3], [1, 2, 4]], [[2, 1], [4, 4]]])); // false