js 零零散散的总结。

    (function(){
        console.log(arguments);  //[] 是一个类数组
        console.log(arguments instanceof Array);//false
        console.log(typeof arguments);// object
    var _arguments = Array.prototype.slice.call(arguments);
        console.log(_arguments); // [] 数组
        console.log(_arguments instanceof Array);//true
        console.log(typeof _arguments); //object
})();

var flatten = matrix.reduce(function (previous, current) {
  return previous.concat(current);
});
console.log(flatten); //[1,2,3,4,5,6]

var sum = [1, 2, 3, 4].reduce(function (previous, current, index, array) {
  return previous + current;
});

console.log(sum); // 10

if (typeof Array.prototype.reduce != "function") {
  Array.prototype.reduce = function (callback, initialValue ) {
     var previous = initialValue, k = 0, length = this.length;
     if (typeof initialValue === "undefined") {
        previous = this[0];
        k = 1;
     }
     
    if (typeof callback === "function") {
      for (k; k < length; k++) {
         this.hasOwnProperty(k) && (previous = callback(previous, this[k], k, this));
      }
    }
    return previous;
  };
}