Javascript：太多的递归错误

Question

I've been working on this project, and I have this array set up that I populate with the following:

var myArray = {};
myArray[idNumber] = parentIdNumber;

Each member can only have one or no parent, denoted by 0. I have values up to 70 filled out.

I'm receiving a value input and need to check if every member of the array is in the 'family line' of input .

So I iterate through myArray and call isInFamilyLine(currentObject, 37) , where currentObject is in the range 1-70:

function isInFamilyLine(idNumber, input) {
    if (idNumber== input) {
        isInLine =  true;
    } else {
        if (myArray[idNumber] == 0) {
            isInLine =   false;
        } else {
            isInLine = isInFamilyLine(myArray[idNumber], input);
        }
    }
    return isInLine;
}

I think the logic is right, but most examples I've seen of too much recursion involved a bug in the code.

What's also weird is that the too much recursion error is thrown on this line:

if (myArray[idNumber] == 0) {

Any ideas?

Answer 1

Given your code, what probably happens is, due to the bad input, nothing gets executed except your next call to isInFamilyLine which is also passed a bad parameter, giving rise to new calls to itself ad nauseum.

If myArray is an associative array, you need to make sure the values for the keys you're passing are of the proper type. You also need to check that whatever you're passing into the function turns out the way you want it and that you don't have any out-of-bounds issues with your array.

Answer 2

I see two possible problems:

Invalid input (thanks IvyLynx )

isInFamilyLine(x, "peanuts") leads to infinite recursion because x != "peanuts" for any sensible value of x and myArray["peanuts"] != 0 because undefined != 0 . This leads to this line always being called:

isInLine = isInFamilyLine(myArray[idNumber], input);

So we have an infinite loop. Solution is to check if myArray[input] === undefined , then throwing an error and asking the user for a new value. This also ensure the input is within the expected range.

Note that because Javascript is weakly typed and you are using == instead of === , "2" == 2 , so receiving input numbers as string should not be the source of the problem.

Circular Structure

If myArray[x] == [x] for any x this code will also go into infinite recursion. You assume the values are acyclic but this may not be true. The same problem happen with cycles of any size, for example

myArray[1] = 2
myArray[2] = 3
myArray[3] = 1

If you only have 70 values a simple solution is to remember which members you have visited and to throw an error if you ever reach the same member twice. Or you could run a check before accepting any inputs, see How do I check if a directed graph is acyclic .

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PS: I'm not sure but I think this algorithm is equivalent to verifying if every node in a tree is reachable or can reach a given input node. Modelling your data as an actual tree and using standard graph algorithms may help.