// declaration of a two-dimensional array
// 5 is the number of rows and 4 is the number of columns.
const matrix = new Array(5).fill(0).map(() => new Array(4).fill(0));
console.log(matrix[0][0]); // 0
const m = 4;
const n = 5;
let arr = new Array(m); // create an empty array of length n
for (var i = 0; i < m; i++) {
arr[i] = new Array(n); // make each element an array
}
console.log(arr); // Output: [ [ <5 empty items> ], [ <5 empty items> ], [ <5 empty items> ], [ <5 empty items> ] ]
var obj = {};
obj['fred'] = {};
if('fred' in obj ){ } // can check for the presence of 'fred'
if(obj.fred) { } // also checks for presence of 'fred'
if(obj['fred']) { } // also checks for presence of 'fred'
// The following statements would all work
obj['fred']['apples'] = 1;
obj.fred.apples = 1;
obj['fred'].apples = 1;
// or build or initialize the structure outright
var obj = { fred: { apples: 1, oranges: 2 }, alice: { lemons: 1 } };