dictdiffer.js

/**
 * This function will take a patch (diffResult) object, as defined by the Python dictdiffer module:
 * 		https://dictdiffer.readthedocs.io/en/latest/
 * and will patch the destination JavaScript object. This is very useful when sending changes to objects shared between
 * Python code and JavaScript code, like through a websocket connection.
 *
 * @param {object} diffResult - the output from the Python function dictdiffer.diff()
 * @param {object} destination - the target JavaScript object. Note that prior to changes the dictionary on the Python
 *                               side must match the JavaScript object. It is a one-way patch
 *                               (Python dict -> JavaScript object).
 * @returns {object} - returns the patched object. While not strictly necessary because the destination object is
 *                     directly updated, it's useful to return the object in some scenarios.
 */
export function patch(diffResult, destination) {
  function dotLookup(source, lookup, parent = false) {
    if (!lookup) {
      return source;
    }
    let value = source;
    let keys;
    if (Array.isArray(lookup)) {
      // the lookup is a list of keys
      keys = [...lookup];
    } else if (typeof lookup === 'string' || lookup instanceof String) {
      // the lookup is a string, split by "."
      keys = lookup.split('.');
    } else {
      throw new Error(
        'function dotLookup requires that the lookup parameter be either a string or an array'
      );
    }
    if (parent) {
      // Remove the last key
      keys.pop();
    }
    keys.forEach((key, index, array) => {
      if (Array.isArray(value)) {
        key = parseInt(key);
      }
      value = value[key];
    });
    return value;
  }

  function add(node, changes) {
    for (let idx = 0; idx < changes.length; idx++) {
      let key = changes[idx][0];
      let value = changes[idx][1];
      let dest = dotLookup(destination, node);
      if (Array.isArray(dest)) {
        dest.splice(key, 0, value);
      } else {
        dest[key] = value;
      }
    }
  }

  function change(node, changes) {
    let dest = dotLookup(destination, node, true);
    let lastNode;
    if (Array.isArray(node)) {
      lastNode = node.pop();
    } else {
      lastNode = node.split('.').pop();
    }
    if (Array.isArray(dest)) {
      lastNode = parseInt(lastNode);
    }
    dest[lastNode] = changes.pop();
  }

  function remove(node, changes) {
    for (let idx = 0; idx < changes.length; idx++) {
      let key = changes[idx][0];
      let dest = dotLookup(destination, node);
      if (Array.isArray(dest)) {
        dest.splice(key, 1);
      } else {
        delete dest[key];
      }
    }
  }

  for (let idx = 0; idx < diffResult.length; idx++) {
    let action = diffResult[idx][0];
    let node = diffResult[idx][1];
    let changes = diffResult[idx][2];
    if (action === 'add') {
      add(node, changes);
    }
    if (action === 'change') {
      change(node, changes);
    }
    if (action === 'remove') {
      remove(node, changes);
    }
  }

  return destination;
}

/**
 * This function will just run some tests against this library.
 */
function runTests() {
  let testObject1 = { a: { b: { c: 3, list: [1, 2] } }, y: [100, 200, 300], remove_this: 'blah' };
  let testObject2 = { a: { b: { c: 1, d: 2, list: [3, 4, 5] } }, z: 1000, y: [100, 200] };
  let diffList = [
    ['change', ['a', 'b', 'list', 0], [1, 3]],
    ['change', ['a', 'b', 'list', 1], [2, 4]],
    ['change', 'a.b.c', [3, 1]],
    ['add', 'a.b.list', [[2, 5]]],
    ['add', 'a.b', [['d', 2]]],
    ['remove', 'y', [[2, 300]]],
    ['add', '', [['z', 1000]]],
    ['remove', '', [['remove_this', 'blah']]]
  ];

  console.log('testObject1: ' + JSON.stringify(testObject1));
  console.log('testObject2: ' + JSON.stringify(testObject2));
  console.log('diffList: ' + JSON.stringify(diffList));

  patch(diffList, testObject1);

  console.log('Patch complete');
  console.log('testObject1: ' + JSON.stringify(testObject1));
  console.log('testObject2: ' + JSON.stringify(testObject2));
}