js校验是否是数组

var is_array = function(value){
    return Object.prototype.toString.apply(value) == '[object Array]';
}

var b = [];

document.writeln(is_array(b));

Array.isArray(b) // 也可以使用

 指定数组的初始值

 Array.dim = function(dimension,initial){
     var a = [], i;

     for(i = 0; i < dimension; i++){
         a[i] = initial;
     }
     return a;
 }

var myArray =  Array.dim(10,"address");

 for(var i in myArray){
     document.writeln(myArray[i]);
 }

   js如何构建一个二维数组

Array.matrix = function (m, n, initial) {
    var a , i, j, mat = [];
    for(i = 0; i < m; i++){
         a = [];
         for(j = 0; j < n; j++){
             a[j] = initial;
         }
         mat[i] = a;
    }
    return mat;
}

js构建一个矩阵

Array.identity = function (n){
    var i, mat = Array.matrix(n, n, 0);
    for(i = 0; i < n; i++){
        mat[i][i] = 4;
    }
    return mat;
}
myMatrix = Array.identity(4);
document.writeln(myMatrix[3][3]);