How can I get a list of the differences between two JavaScript object graphs?

Question

I want to be able to get a list of all differences between two JavaScript object graphs, with the property names and values where the deltas occur.

For what it is w

Answer 1

Solution 1

Use JSON.stringify(obj) to get a string representation of the objects you want to compare. Save the string to a file. Use any diff viewer to compare the text files.

Note: JSON.stringify will ignore properties that point to function definitions.

Solution 2

This could do what you want with some modification, it is a modified version of the function _.isEqual (http://documentcloud.github.com/underscore/). Please feel free to suggest any modifications! I wrote it to figure out where the first difference between two objects occur.

// Given two objects find the first key or value not matching, algorithm is a
// inspired by of _.isEqual.
function diffObjects(a, b) {
  console.info("---> diffObjects", {"a": a, "b": b});
  // Check object identity.
  if (a === b) return true;
  // Different types?
  var atype = typeof(a), btype = typeof(b);
  if (atype != btype) {
    console.info("Type mismatch:", {"a": a, "b": b});
    return false;
  };
  // Basic equality test (watch out for coercions).
  if (a == b) return true;
  // One is falsy and the other truthy.
  if ((!a && b) || (a && !b)) {
    console.info("One is falsy and the other truthy:", {"a": a, "b": b});
    return false;
  }
  // Unwrap any wrapped objects.
  if (a._chain) a = a._wrapped;
  if (b._chain) b = b._wrapped;
  // One of them implements an isEqual()?
  if (a.isEqual) return a.isEqual(b);
  // Check dates' integer values.
  if (_.isDate(a) && _.isDate(b)) return a.getTime() === b.getTime();
  // Both are NaN?
  if (_.isNaN(a) && _.isNaN(b)) {
    console.info("Both are NaN?:", {"a": a, "b": b});
    return false;
  }
  // Compare regular expressions.
  if (_.isRegExp(a) && _.isRegExp(b))
    return a.source     === b.source &&
           a.global     === b.global &&
           a.ignoreCase === b.ignoreCase &&
           a.multiline  === b.multiline;
  // If a is not an object by this point, we can't handle it.
  if (atype !== 'object') {
    console.info("a is not an object:", {"a": a});
    return false;
  }
  // Check for different array lengths before comparing contents.
  if (a.length && (a.length !== b.length)) {
    console.info("Arrays are of different length:", {"a": a, "b": b});
    return false;
  }
  // Nothing else worked, deep compare the contents.
  var aKeys = _.keys(a), bKeys = _.keys(b);
  // Different object sizes?
  if (aKeys.length != bKeys.length) {
    console.info("Different object sizes:", {"a": a, "b": b});
    return false;
  }
  // Recursive comparison of contents.
  for (var key in a) if (!(key in b) || !diffObjects(a[key], b[key])) return false;
  return true;
};