batteries/lib/repr.js

// batteries
// Copyright 2010 - 2011 Sami Samhuri <sami@samhuri.net>

// readable string representations of values
exports.repr = repr;

exports.extendNative = function(context) {
  context.repr = repr;
};

function repr(x) {
  if (x !== null && x !== undefined && typeof x.repr === 'function') return x.repr();

  var nativeToStringIsReadable =
         x === null
      || x === undefined
      || x instanceof Number
      || typeof x === 'number'
      || x instanceof Boolean
      || typeof x === 'boolean'
      || x instanceof RegExp
      || x.constructor === RegExp;

  if (nativeToStringIsReadable) {
    return String(x);
  }

  if (x instanceof String || typeof x === 'string') {
    return '"' + x.replace(/"/g, '\\"') + '"';
  }

  if (x instanceof Date || x.toUTCString) {
    return 'new Date(' + (+x) + ')'; // lame
  }

  if (Array.isArray(x)) {
    return '[' + x.map(repr).join(',') + ']';
  }

  if (x instanceof Function || typeof x === 'function') {
    return x.toString();
  }

  // TODO determine how far to go with this. should we include non-enumerable props too?
  if (x instanceof Object || typeof x === 'object') {
    return '{' + Object.keys(x).map(function(k) { return repr(k) + ':' + repr(x[k]); }).join(',') + '}';
  }

  throw new Error("don't know how to represent " + x);
}