不可变数据更新

gistfile1.js

var DIRECTIVE_SET      = '$set';
var DIRECTIVE_PUSH     = '$push';
var DIRECTIVE_UNSHIFT  = '$unshift';
var DIRECTIVE_SPLICE   = '$splice';
var DIRECTIVE_MERGE    = '$merge';
var ALL_DIRECTIVES_SET = {};

ALL_DIRECTIVES_SET[DIRECTIVE_SET]     = true;
ALL_DIRECTIVES_SET[DIRECTIVE_PUSH]    = true;
ALL_DIRECTIVES_SET[DIRECTIVE_UNSHIFT] = true;
ALL_DIRECTIVES_SET[DIRECTIVE_SPLICE]  = true;
ALL_DIRECTIVES_SET[DIRECTIVE_MERGE]   = true;

function copyProperties(obj, obj1) {
  obj = obj || {};
  for (var k in obj1) {
    if (obj1.hasOwnProperty(k)) {
      obj[k] = obj1[k];
    }
  }
  return obj;
}

function shallowCopy(e) {
  if (Object.prototype.toString.call(e) == '[object Array]') {
    return e.concat();
  } else if (typeof e == 'object') {
    return copyProperties({}, e);
  } else {
    return e;
  }
}

function immutableUpdate(value, spec) {
  if (spec.hasOwnProperty(DIRECTIVE_SET)) {
    return spec[DIRECTIVE_SET];
  }
  
  var nextValue = shallowCopy(value);
  var specValue;
  
  if (spec.hasOwnProperty(DIRECTIVE_PUSH)) {
    specValue = spec[DIRECTIVE_PUSH];
    if (Object.prototype.toString.call(specValue) == '[object Array]') {
      nextValue = nextValue.concat(specValue);
    } else {
      nextValue.push(specValue);
    }
  }

  if (spec.hasOwnProperty(DIRECTIVE_UNSHIFT)) {
    specValue = spec[DIRECTIVE_UNSHIFT];
    if (Object.prototype.toString.call(specValue) == '[object Array]') {
      nextValue.splice.apply(nextValue, [0,0].concat(specValue));
    } else {
      nextValue.unshift(specValue);
    }
  }
  
  if (spec.hasOwnProperty(DIRECTIVE_SPLICE)) {
    nextValue.splice.apply(nextValue, spec[DIRECTIVE_SPLICE]);
  }

  if (spec.hasOwnProperty(DIRECTIVE_MERGE)) {
    nextValue = copyProperties(nextValue, spec[DIRECTIVE_MERGE]);
  }
  
  for (var k in spec) {
    if (!ALL_DIRECTIVES_SET.hasOwnProperty(k)) {
      nextValue[k] = immutableUpdate(value[k], spec[k]);
    }
  }
  
  return nextValue;
}

/*

var foo = {
  x: 10,
  y: {
    x1: [1, 2, 3],
    y1: { x2: 'foo1' }
  }
};

console.log('update result:',
  immutableUpdate(foo, 
        {
          x: { $set: 20 },
          y: { 
            x1: { $push: {x: 0} },
            y1: { $merge: { x2: 'updated!' }
             }
          }
        }
      )
);

//返回结果:
{
  x: 20,
  y: {
    x1: [1, 2, 3, {x:0}],
    y1: { x2: 'updated' }
  }
}

console.log('result', foo);
// foo 属性不变
var foo = {
  x: 10,
  y: {
    x1: [1, 2, 3],
    y1: { x2: 'foo1' }
  }
};


*/