index.js

/**
 * Module Dependencies
 */

var expr;
try {
  expr = require('props');
} catch(e) {
  expr = require('component-props');
}

/**
 * Expose `toFunction()`.
 */

module.exports = toFunction;

/**
 * Convert `obj` to a `Function`.
 *
 * @param {Mixed} obj
 * @return {Function}
 * @api private
 */

function toFunction(obj) {
  switch ({}.toString.call(obj)) {
    case '[object Object]':
      return objectToFunction(obj);
    case '[object Function]':
      return obj;
    case '[object String]':
      return stringToFunction(obj);
    case '[object RegExp]':
      return regexpToFunction(obj);
    default:
      return defaultToFunction(obj);
  }
}

/**
 * Default to strict equality.
 *
 * @param {Mixed} val
 * @return {Function}
 * @api private
 */

function defaultToFunction(val) {
  return function(obj){
    return val === obj;
  };
}

/**
 * Convert `re` to a function.
 *
 * @param {RegExp} re
 * @return {Function}
 * @api private
 */

function regexpToFunction(re) {
  return function(obj){
    return re.test(obj);
  };
}

/**
 * Convert property `str` to a function.
 *
 * @param {String} str
 * @return {Function}
 * @api private
 */

function stringToFunction(str) {
  // immediate such as "> 20"
  if (/^ *\W+/.test(str)) return new Function('_', 'return _ ' + str);

  // properties such as "name.first" or "age > 18" or "age > 18 && age < 36"
  return new Function('_', 'return ' + get(str));
}

/**
 * Convert `object` to a function.
 *
 * @param {Object} object
 * @return {Function}
 * @api private
 */

function objectToFunction(obj) {
  var match = {};
  for (var key in obj) {
    match[key] = typeof obj[key] === 'string'
      ? defaultToFunction(obj[key])
      : toFunction(obj[key]);
  }
  return function(val){
    if (typeof val !== 'object') return false;
    for (var key in match) {
      if (!(key in val)) return false;
      if (!match[key](val[key])) return false;
    }
    return true;
  };
}

/**
 * Built the getter function. Supports getter style functions
 *
 * @param {String} str
 * @return {String}
 * @api private
 */

function get(str) {
  var props = expr(str);
  if (!props.length) return '_.' + str;

  var val, i, prop;
  for (i = 0; i < props.length; i++) {
    prop = props[i];
    val = '_.' + prop;
    val = "('function' == typeof " + val + " ? " + val + "() : " + val + ")";

    // mimic negative lookbehind to avoid problems with nested properties
    str = stripNested(prop, str, val);
  }

  return str;
}

/**
 * Mimic negative lookbehind to avoid problems with nested properties.
 *
 * See: http://blog.stevenlevithan.com/archives/mimic-lookbehind-javascript
 *
 * @param {String} prop
 * @param {String} str
 * @param {String} val
 * @return {String}
 * @api private
 */

function stripNested (prop, str, val) {
  return str.replace(new RegExp('(\\.)?' + prop, 'g'), function($0, $1) {
    return $1 ? $0 : val;
  });
}