index.js

/**
 * Module dependencies.
 */

try {
  var type = require('type');
} catch (err) {
  var type = require('component-type');
}

var toFunction = require('to-function');

/**
 * HOP reference.
 */

var has = Object.prototype.hasOwnProperty;

/**
 * Iterate the given `obj` and invoke `fn(val, i)`
 * in optional context `ctx`.
 *
 * @param {String|Array|Object} obj
 * @param {Function} fn
 * @param {Object} [ctx]
 * @api public
 */

module.exports = function(obj, fn, ctx){
  fn = toFunction(fn);
  ctx = ctx || this;
  switch (type(obj)) {
    case 'array':
      return array(obj, fn, ctx);
    case 'object':
      if ('number' == typeof obj.length) return array(obj, fn, ctx);
      return object(obj, fn, ctx);
    case 'string':
      return string(obj, fn, ctx);
  }
};

/**
 * Iterate string chars.
 *
 * @param {String} obj
 * @param {Function} fn
 * @param {Object} ctx
 * @api private
 */

function string(obj, fn, ctx) {
  for (var i = 0; i < obj.length; ++i) {
    fn.call(ctx, obj.charAt(i), i);
  }
}

/**
 * Iterate object keys.
 *
 * @param {Object} obj
 * @param {Function} fn
 * @param {Object} ctx
 * @api private
 */

function object(obj, fn, ctx) {
  for (var key in obj) {
    if (has.call(obj, key)) {
      fn.call(ctx, key, obj[key]);
    }
  }
}

/**
 * Iterate array-ish.
 *
 * @param {Array|Object} obj
 * @param {Function} fn
 * @param {Object} ctx
 * @api private
 */

function array(obj, fn, ctx) {
  for (var i = 0; i < obj.length; ++i) {
    fn.call(ctx, obj[i], i);
  }
}