Nodejs: how to clone an object

Question

If I clone an array, I use cloneArr = arr.slice()

I want to know how to clone an object in nodejs.

Answer 1

There is no native method for cloning objects. Underscore implements _.clone which is a shallow clone.

_.clone = function(obj) {
  return _.isArray(obj) ? obj.slice() : _.extend({}, obj);
};

It either slices it or extends it.

Here's _.extend

// extend the obj (first parameter)
_.extend = function(obj) {
  // for each other parameter
  each(slice.call(arguments, 1), function(source) {
    // loop through all properties of the other objects
    for (var prop in source) {
      // if the property is not undefined then add it to the object.
      if (source[prop] !== void 0) obj[prop] = source[prop];
    }
  });
  // return the object (first parameter)
  return obj;
};

Extend simply iterates through all the items and creates a new object with the items in it.

You can roll out your own naive implementation if you want

function clone(o) {
  var ret = {};
  Object.keys(o).forEach(function (val) {
    ret[val] = o[val];
  });
  return ret;
}

There are good reasons to avoid deep cloning because closures cannot be cloned.

I've personally asked a question about deep cloning objects before and the conclusion I came to is that you just don't do it.

My recommendation is use underscore and it's _.clone method for shallow clones