Mutual recursion and JSLint - function was used before it was defined

Question

If I write the following code, JSLint complains that 'isOdd' was used before it was defined. Is there a way to write mutually recursive code and still please JSLint?

var isEven = function(n) {
    if (n === 0) {
        return true;
    }
    return isOdd(n - 1);
};

var isOdd = function(n) {
    if (n === 0) {
        return false;
    }
    return isEven(n - 1);
};

@JaromandaX JSLint still complains even if I use that format — johnnyodonnell, Aug 22 '17 at 02:37
`var isOdd;` before `var isEven = ...` then remove `var` from your `var isOdd` — Jaromanda X, Aug 22 '17 at 02:46
You should remove JSLint from your computer, stab it in the heart, break it into little pieces, burn those pieces, and then bury them. It was never a good tool, and now it's obsolete. — , Aug 22 '17 at 03:05

score 4 · Answer 1 · answered Aug 22 '17 at 02:54

For JSLint, you have to add a global variables directive to the top of the file, so that it ignores usage of temporary "undefined" functions and variables.

/*global isOdd */

var isEven = function(n) {
    if (n === 0) {
        return true;
    }
    return isOdd(n - 1);
};

var isOdd = function(n) {
    if (n === 0) {
        return false;
    }
    return isEven(n - 1);
};

You could also declare isOdd at the top, but then you would change your actual code because a linting program doesn't understand hoisting:

var isOdd;

var isEven = function(n) {
    if (n === 0) {
        return true;
    }
    return isOdd(n - 1);
};

isOdd = function(n) {
    if (n === 0) {
        return false;
    }
    return isEven(n - 1);
};

score 1 · Accepted Answer · answered Aug 23 '17 at 20:38

Converting these functions to methods of an object quell the error message from JSLint. This also does a better job of keeping the global namespace less polluted.

var numUtil = {
    isEven: function(n) {
        if (n === 0) {
            return true;
        }
        return this.isOdd(n - 1);
    },
    isOdd: function(n) {
        if (n === 0) {
            return false;
        }
        return this.isEven(n - 1);
    }
};

Mutual recursion and JSLint - function was used before it was defined

2 Answers2

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