Slice like Ruby for JavaScript

slicer.js

(function(exports) {
"use strict";

/**
 * arr["1..3"]かarr["1,2,3"]という形式かを判断する
 * @private
 */
function sliceInfo(str) {
  var

  //arr["1..3"]という形式
  m = str.match(/^([+-]?\d+)\.\.([+-]?\d+)$/);
  if (m !== null)  {
    return {
      type: "range",
      indexes: [parseInt(m[1],10),parseInt(m[2],10)],
    };
  }

  //arr["1,2,3"]という形式
  m = str.split(",");
  if (m.length > 1) {
    return {
      type: "multi",
      indexes: m
    };
  }

  //どれでもなかった
  return null;
}

/**
 * getハンドラの実体
 * @private
 */
function get(arr,str) {
  var
  info = sliceInfo(str);

  if (!info) {
/*    //Arrayのメソッドの場合は正しく呼び出せるようbind
    return typeof arr[str] === "function" && isNaN(parseInt(str)) ? arr[str].bind(arr) : arr[str];
*/
    //なんか大丈夫っぽい
    //TODO: 何で大丈夫になったのか考える
    return arr[str];
  }

  switch (info.type) {
  case "range":
    return arr.slice(info.indexes[0],info.indexes[1]+1);
  case "multi":
    return info.indexes.map(function(i) {
      return arr[i];
    });
  }
}

/**
 * setハンドラの実体
 * @private
 */
function set(arr,str,val) {
  var
  //valがプリミティブ値かどうか
  isprim = typeof val !== "object" && val === null,
  a,b,
  info = sliceInfo(str);

  if (!info) {
    arr[str] = val;
  } else {
    switch (info.type) {
    case "range":
      a = info.indexes[0];
      a = a < 0 ? arr.length - a : a;
      b = info.indexes[1];
      b = (b < 0 ? arr.length - b : b) - a + 1;
      arr.splice.apply(arr,[a,b].concat(val));
      break;
    case "multi":
      if (isprim) {
        info.indexes.forEach(function(i) {
          arr[i] = val;
        });
      } else {
        info.indexes.forEach(function(i,j) {
          arr[i] = val[j];
        });
      }
      break;
    }
  }
}

/**
 * hasハンドラの実体
 * @private
 */
function has(arr,str) {
  var
  info = sliceInfo(str),
  a,b;

  switch (info && info.type) {
  case null:
    return str in arr;

  case "range":
    a = info.indexes[0];
    a = a < 0 ? arr.length - a : a;
    b = info.indexes[0];
    b = b < 0 ? arr.length - b : b;
    return a < arr.length && b <= arr.length;

  case "multi":
    return info.indexes.every(function(i) {
      return i in arr;
    });
  }
}

/**
 * deleteハンドラの実体
 * @private
 */
function delete_(arr,str) {
  var
  info = sliceInfo(str),
  a,b,i;
  
  switch (info && info.type) {
  case null:
    return delete arr[str];

  case "range":
    a = info.indexes[0];
    a = a < 0 ? arr.length - a : a;
    b = info.indexes[1];
    b = b < 0 ? arr.length - b : b;
    for (i = a;i <= b;i++) {
      delete arr[i];
    }
    break;

  case "multi":
    info.indexes.forEach(function(i) {
      delete arr[i];
    });
    break;
  }
  
  return true;
}

/**
 * スライス操作できるように配列を拡張する
 * @param arr {Array} 拡張する配列
 * @return {Slicer}
 */
function toSlicer(arr) {
  var
  handler = createHandler(arr);
  
  return Proxy.create(handler);
}

/**
 * @private
 */
function createHandler(arr) {
  return {
    //arr[name]
    get: function(_,name) {
      return get(arr,name);
    },
    //arr[name] = val
    set: function(_,name,val) {
      set(arr,name,val);
    },
    //name in arr
    has: function(name) {
      return has(arr,name);
    },
    hasOwn: function(name) {
      return Object.prototype.hasOwnProperty(arr,name);
    },
    // delete arr[name];
    delete: function(name) {
      return delete_(arr,name);
    },
    getPropertyDescripter: function(name) {
      return Object.getPropertyDescripter(arr,name);
    },
    getOwnPropertyDescripter: function(name) {
      return Object.getOwnPropertyDescripter(arr,name);
    },
    getOwnPropertyNames: function() {
      return Object.getOwnPropertyNames(arr);
    },
    getPropertyNames: function() {
      return Object.getPropertyNames(arr);
    },
    fix: function() {
      if(Object.isFrozen(arr)) {
        return Object.getOwnPropertyNames(arr).map(function(name) {
          return Object.getOwnPropertyDescriptor(arr, name);
        });
      }
      return undefined;
    },
    enumerate: function() {
      var res = [];
      for (var name in arr) {
        res.push(name);
      }
      return res;
    },
    keys: function() {
      return Object.keys(arr);
    },
  };
}

//export
exports.toSlicer = toSlicer;
})(typeof this.exports !== "undefined" ? this.exports : this);

test.js

var
arr = [1,2,3,4,5],
sli = toSlicer(arr);

console.log(sli["1..3"]);  // 2,3,4
console.log(sli["0,2,4"]); // 1,3,5

sli["1..3"] = [6,7,8];
sli["2,4"] = sli["4,2"];

sli.push(9);

console.log(sli); // 1,6,5,8,7,9