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

Question

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.

that would check `w[1][2][1][3]` value is the text "undefined" — Patrick Evans, Jun 02 '13 at 14:06
@Patrick Evans, it returns error: TypeError: w[w1][w2][w3] is undefined in code: if (typeof w[w1][w2][w3][w4] != 'undefined') { return w[w1][w2][w3][w4]; } — Colargol, Jun 02 '13 at 14:20
then you need to check each previous array element for existence before checking the others. — Patrick Evans, Jun 02 '13 at 14:22
@Patrick Evans, thanks it works: if (typeof w[w1][w2][w3] != 'undefined' && typeof w[w1][w2][w3][w4] != 'undefined') — Colargol, Jun 02 '13 at 14:28
possible duplicate of [In JavaScript, is there an easier way to check if a property of a property exists?](http://stackoverflow.com/questions/7636789/in-javascript-is-there-an-easier-way-to-check-if-a-property-of-a-property-exist) — Felix Kling, Jun 02 '13 at 14:35

score 6 · Accepted Answer · answered Jun 02 '13 at 14:30

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.

basilikum · Answer 2 · 2013-06-02T14:51:38.303

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

I was unable to get your check function to work. See my test code below. I added a workaround below your 'check' that did work for me. — Tom McDonald, May 10 '16 at 17:50

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

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