Question

I know my ‘algorithm’ isn’t useful at all, but I think I encountered a very strange behaviour.

findMatching([“jokes”,”jokeg”],”jokes”); returns jokes. But findMatching([“jokes”,”jokeg”,”jokef”],”jokes”); returns jokes and jokef! When I individually test jokef it does not match.

Here is my code:

        for (var p in dataArray) {
            if (dataArray[p].length != matching.length) {
                dataArray.splice(p,1);
            }
        }
        for (var k = 0; k < matching.length; k++) {
            for (var i in dataArray) {
                if (dataArray[i].split('')[k] != matching.split('')[k]) {
                    dataArray.splice(i,1);
                }
            }
        }
        if(dataArray.length == 0){
            return null;
        } else {
            return dataArray;
        }

Answer 1

Array.splice() is a destructive operation that alters the length of an array. This can clearly be seen if you add a console.log statement to your middle for loop:

for (var k = 0; k < matching.length; k++) {
    for (var i in dataArray) {
        console.log(dataArray, i, k, dataArray[i].split('')[k], matching.split('')[k]);
        if (dataArray[i].split('')[k] != matching.split('')[k]) {
            dataArray.splice(i,1);
        }
    }
}

The output should look something like this:

["jokes", "jokeg", "jokef"] 0 0 j j
["jokes", "jokeg", "jokef"] 1 0 j j
["jokes", "jokeg", "jokef"] 2 0 j j
["jokes", "jokeg", "jokef"] 0 1 o o
["jokes", "jokeg", "jokef"] 1 1 o o
["jokes", "jokeg", "jokef"] 2 1 o o
["jokes", "jokeg", "jokef"] 0 2 k k
["jokes", "jokeg", "jokef"] 1 2 k k
["jokes", "jokeg", "jokef"] 2 2 k k
["jokes", "jokeg", "jokef"] 0 3 e e
["jokes", "jokeg", "jokef"] 1 3 e e
["jokes", "jokeg", "jokef"] 2 3 e e
["jokes", "jokeg", "jokef"] 0 4 s s
["jokes", "jokeg", "jokef"] 1 4 g s

It never gets to the ‘f’ in “jokef” because it spliced the array. matching.length is now 2 and the for condition (var k = 0; k < matching.length; k++) is now false, causing the loop to break and the JavaScript engine to move onto the next block.