unist-util-visit/index.js

/**
 * @author Titus Wormer
 * @copyright 2015 Titus Wormer. All rights reserved.
 * @module unist:util:visit
 * @fileoverview Utility to recursively walk over unist nodes.
 */

'use strict';

/**
 * Walk forwards.
 *
 * @param {Array.<*>} values - Things to iterate over,
 *   forwards.
 * @param {function(*, number): boolean} callback - Function
 *   to invoke.
 * @return {boolean} - False if iteration stopped.
 */
function forwards(values, callback) {
    var index = -1;
    var length = values.length;

    while (++index < length) {
        if (callback(values[index], index) === false) {
            return false;
        }
    }

    return true;
}

/**
 * Walk backwards.
 *
 * @param {Array.<*>} values - Things to iterate over,
 *   backwards.
 * @param {function(*, number): boolean} callback - Function
 *   to invoke.
 * @return {boolean} - False if iteration stopped.
 */
function backwards(values, callback) {
    var index = values.length;
    var length = -1;

    while (--index > length) {
        if (callback(values[index], index) === false) {
            return false;
        }
    }

    return true;
}

/**
 * Visit.
 *
 * @param {Node} tree - Root node
 * @param {string} [type] - Node type.
 * @param {function(node): boolean?} callback - Invoked
 *   with each found node.  Can return `false` to stop.
 * @param {boolean} [reverse] - By default, `visit` will
 *   walk forwards, when `reverse` is `true`, `visit`
 *   walks backwards.
 */
function visit(tree, type, callback, reverse) {
    var iterate;
    var one;
    var all;

    if (typeof type === 'function') {
        reverse = callback;
        callback = type;
        type = null;
    }

    iterate = reverse ? backwards : forwards;

    /**
     * Visit `children` in `parent`.
     */
    all = function (children, parent) {
        return iterate(children, function (child, index) {
            return child && one(child, index, parent);
        });
    };

    /**
     * Visit a single node.
     */
    one = function (node, index, parent) {
        var result;

        index = index || (parent ? 0 : null);

        if (!type || node.type === type) {
            result = callback(node, index, parent || null);
        }

        if (node.children && result !== false) {
            return all(node.children, node);
        }

        return result;
    };

    one(tree);
}

/*
 * Expose.
 */

module.exports = visit;