How to check if a multidimensional array item is set in JS?

Question

How to check if a multidimensional array item is set in JS?

w[1][2] = new Array;
w[1][2][1] = new Array;
w[1][2][1][1] = 10; w[1][2][1][2] = 20; w[1][2][1][4] = 30;

How to check if w[1][2][1][3] is set?

Solution with if (typeof w[1][2][1][3] != 'undefined') doesn't work.

I don't want to use an Object instead of Array.

Answer 1

You are not checking the previous array elements existence before checking its children as the children elements cant exist if the parent doesnt

if( 
    typeof(w) != 'undefined' &&
    typeof(w[1]) != 'undefined' &&
    typeof(w[1][2]) != 'undefined' &&
    typeof(w[1][2][1]) != 'undefined' &&
    typeof(w[1][2][1][3]) != 'undefined' &&
  ) {
    //do your code here if it exists  
  } else {
    //One of the array elements does not exist
  }

The if will run the code in the else clause if it sees any of the previous elements not existing. It stops checking the others if any of the preceding checks returns false.

Answer 2

Here is a more generic way you can do it by extending the prototype of Array:

Array.prototype.check = function() {
    var arr = this, i, max_i;
    for (i = 0, max_i = arguments.length; i < max_i; i++) {
        arr = arr[arguments[i]];
        if (arr === undefined) {
            return false;
        }
    }
    return true;    
}

w.check(1, 2, 1, 4); //will be true if w[1][2][1][4] exists

or if you don't like prototype extension you could use a separate function:

function check(arr) {
    var i, max_i;
    for (i = 1, max_i = arguments.length; i < max_i; i++) {
        arr = arr[arguments[i]];
        if (arr === undefined) {
            return false;
        }
    }
    return true;
}

check(w, 1, 2, 1, 4); //will be true if w[1][2][1][4] exists