handlebars.js/lib/handlebars/utils.js

var toString = Object.prototype.toString,
    isArray = Array.isArray;

var errorProps = ['description', 'fileName', 'lineNumber', 'message', 'name', 'number', 'stack'];

export function Exception(message) {
  var tmp = Error.prototype.constructor.apply(this, arguments);

  // Unfortunately errors are not enumerable in Chrome (at least), so `for prop in tmp` doesn't work.
  for (var idx = 0; idx < errorProps.length; idx++) {
    this[errorProps[idx]] = tmp[errorProps[idx]];
  }
};

Exception.prototype = new Error();

// Build out our basic SafeString type
export function SafeString(string) {
  this.string = string;
};

SafeString.prototype.toString = function() {
  return "" + this.string;
};

var escape = {
  "&": "&amp;",
  "<": "&lt;",
  ">": "&gt;",
  '"': "&quot;",
  "'": "&#x27;",
  "`": "&#x60;"
};

var badChars = /[&<>"'`]/g;
var possible = /[&<>"'`]/;

var escapeChar = function(chr) {
  return escape[chr] || "&amp;";
};

export function extend(obj, value) {
  for(var key in value) {
    if(value.hasOwnProperty(key)) {
      obj[key] = value[key];
    }
  }
}

export function escapeExpression(string) {
  // don't escape SafeStrings, since they're already safe
  if (string instanceof SafeString) {
    return string.toString();
  } else if (!string && string !== 0) {
    return "";
  }

  // Force a string conversion as this will be done by the append regardless and
  // the regex test will do this transparently behind the scenes, causing issues if
  // an object's to string has escaped characters in it.
  string = "" + string;

  if(!possible.test(string)) { return string; }
  return string.replace(badChars, escapeChar);
}

export function isEmpty(value) {
  if (!value && value !== 0) {
    return true;
  } else if (isArray(value) && value.length === 0) {
    return true;
  } else {
    return false;
  }
}