index.mjs

/*
  const obj1 = {a: 3, b: 5};
  diffApply(obj1,
    [
      { "op": "remove", "path": ['b'] },
      { "op": "replace", "path": ['a'], "value": 4 },
      { "op": "add", "path": ['c'], "value": 5 }
    ]
  );
  obj1; // {a: 4, c: 5}

  // using converter to apply jsPatch standard paths
  // see http://jsonpatch.com
  import {diff, jsonPatchPathConverter} from 'just-diff'
  const obj2 = {a: 3, b: 5};
  diffApply(obj2, [
    { "op": "remove", "path": '/b' },
    { "op": "replace", "path": '/a', "value": 4 }
    { "op": "add", "path": '/c', "value": 5 }
  ], jsonPatchPathConverter);
  obj2; // {a: 4, c: 5}

  // arrays
  const obj3 = {a: 4, b: [1, 2, 3]};
  diffApply(obj3, [
    { "op": "replace", "path": ['a'], "value": 3 }
    { "op": "replace", "path": ['b', 2], "value": 4 }
    { "op": "add", "path": ['b', 3], "value": 9 }
  ]);
  obj3; // {a: 3, b: [1, 2, 4, 9]}

  // nested paths
  const obj4 = {a: 4, b: {c: 3}};
  diffApply(obj4, [
    { "op": "replace", "path": ['a'], "value": 5 }
    { "op": "remove", "path": ['b', 'c']}
    { "op": "add", "path": ['b', 'd'], "value": 4 }
  ]);
  obj4; // {a: 5, b: {d: 4}}
*/

var REMOVE = 'remove';
var REPLACE = 'replace';
var ADD = 'add';
var MOVE = 'move';

function diffApply(obj, diff, pathConverter) {
  if (!obj || typeof obj != 'object') {
    throw new Error('base object must be an object or an array');
  }

  if (!Array.isArray(diff)) {
    throw new Error('diff must be an array');
  }

  var diffLength = diff.length;
  for (var i = 0; i < diffLength; i++) {
    var thisDiff = diff[i];
    var subObject = obj;
    var thisOp = thisDiff.op;

    var thisPath = transformPath(pathConverter, thisDiff.path);
    var thisFromPath = thisDiff.from && transformPath(pathConverter, thisDiff.from);
    var toPath, toPathCopy, lastToProp, subToObject, valueToMove;

    if (thisFromPath) {
      // MOVE only, "fromPath" is effectively path and "path" is toPath
      toPath = thisPath;
      thisPath = thisFromPath;

      toPathCopy = toPath.slice();
      lastToProp = toPathCopy.pop();
      prototypeCheck(lastToProp);
      if (lastToProp == null) {
        return false;
      }

      var thisToProp;
      while (((thisToProp = toPathCopy.shift())) != null) {
        prototypeCheck(thisToProp);
        if (!(thisToProp in subToObject)) {
          subToObject[thisToProp] = {};
        }
        subToObject = subToObject[thisToProp];
      }
    }

    var pathCopy = thisPath.slice();
    var lastProp = pathCopy.pop();
    prototypeCheck(lastProp);
    if (lastProp == null) {
      return false;
    }

    var thisProp;
    while (((thisProp = pathCopy.shift())) != null) {
      prototypeCheck(thisProp);
      if (!(thisProp in subObject)) {
        subObject[thisProp] = {};
      }
      subObject = subObject[thisProp];
    }
    if (thisOp === REMOVE || thisOp === REPLACE || thisOp === MOVE) {
      var path = thisOp === MOVE ? thisDiff.from : thisDiff.path;
      if (!subObject.hasOwnProperty(lastProp)) {
        throw new Error(['expected to find property', path, 'in object', obj].join(' '));
      }
    }
    if (thisOp === REMOVE || thisOp === MOVE) {
      if (thisOp === MOVE) {
        valueToMove = subObject[lastProp];
      }
      Array.isArray(subObject) ? subObject.splice(lastProp, 1) : delete subObject[lastProp];
    }
    if (thisOp === REPLACE || thisOp === ADD) {
      subObject[lastProp] = thisDiff.value;
    }

    if (thisOp === MOVE) {
      subObject[lastToProp] = valueToMove;
    }
  }
  return subObject;
}

function transformPath(pathConverter, thisPath) {
  if(pathConverter) {
    thisPath = pathConverter(thisPath);
    if(!Array.isArray(thisPath)) {
      throw new Error([
        'pathConverter must return an array, returned:',
        thisPath,
      ].join(' '));
    }
  } else {
    if(!Array.isArray(thisPath)) {
      throw new Error([
        'diff path',
        thisPath,
        'must be an array, consider supplying a path converter']
        .join(' '));
    }
  }
  return thisPath;
}

function jsonPatchPathConverter(stringPath) {
  return stringPath.split('/').slice(1);
}

function prototypeCheck(prop) {
  // coercion is intentional to catch prop values like `['__proto__']`
  if (prop == '__proto__' || prop == 'constructor' || prop == 'prototype') {
    throw new Error('setting of prototype values not supported');
  }
}

export {diffApply, jsonPatchPathConverter};