javascript recursion within an exports function: not a function

Question

perennial newbie question: how do i fix this "not a function" error:

exports.height = (input) => {
    function height(node, height) {
        if (node.left) {
            if (height > maxHeight) {
                maxHeight = height;
            }
            **height(node.left, height+1); // <-- Says "Not a function"**
        }
    }

    var maxHeight = 0;
    height( input, 0 ); // <--- This works fine.

    return maxHeight;
}

says, TypeError: height is not a function

  at height (BinarySearchTree.js:53:5)

Thanks! Nilesh

You named your parameter the same as the function. Did you try debugging with console.log(height)? — user1106925
– user1106925, Commented Nov 2, 2016 at 18:10
@Geeky: exports.height is referencing a different function. There are too many things named height in this code. — user1106925
– user1106925, Commented Nov 2, 2016 at 18:12

Mulan · Accepted Answer · 2016-11-02 18:17:46Z

3

You accidentally shadowed your height variable

function height(node, height) {
    if (node.left) {
        if (height > maxHeight) {
            maxHeight = height;
        }
        height(node.left, height+1);
    }
}

var maxHeight = 0;
height( input, 0 ); // 0 is obviously not a function ^_^

Try renaming the height parameter to something like h

function height(node, h) {
    if (node.left) {
        if (h > maxHeight) {
            maxHeight = h;
        }
        return height(node.left, h+1); // don't forget your return
    }
}

var maxHeight = 0;
height( input, 0 );

All that said, you might want to reconsider your function alltogether

function height (node) {
  if (node === undefined)
    return -1;
  else
    return Math.max(height(node.left), height(node.right)) + 1;
}

edited Nov 2, 2016 at 18:17

answered Nov 2, 2016 at 18:09

Mulan

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Comments

Alexander O'Mara · Accepted Answer · 2016-11-02 18:10:24Z

0

The problem is you've shadowed the function variable named height with an argument of the same name:

function height(node, height) {

Because JavaScript functions are first-class citizens, in the context of the height function body, there is now a local variable named height which is not the same as the function.

Consider changing the name of one of them, like so:

function height(node, h) {
    if (node.left) {
        if (h > maxHeight) {
            maxHeight = h;
        }
        height(node.left, h+1);
    }
}

answered Nov 2, 2016 at 18:10

Alexander O'Mara

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