Underscore.js學習筆記

1. 緩存原型，考慮訪問速度

var
    push             = ArrayProto.push,
    slice            = ArrayProto.slice,
    concat           = ArrayProto.concat,
    toString         = ObjProto.toString,
    hasOwnProperty   = ObjProto.hasOwnProperty;

2. 判斷數組是否支持forEach方法，判斷對象是否有此原型方法

nativeForEach && obj.forEach === nativeForEach

3. Object.keys方法返回對象自身可枚舉的屬性，不一樣於hasOwnProperty方法會繼承上級屬性

4. 函數參數個數多於65535個時，Math.max.apply(Math, array)會發生範圍溢出錯誤

　https://bugs.webkit.org/show_bug.cgi?id=80797

5. 

var arr = [1,2,3,4],
      arr1= [5,6,7,8];
// arr.push.apply(arr,arr1) == arr.push(5,6,7,8)

 6. 數組初始化時，明確長度後再賦值性能較好，參考 http://jsperf.com/array-init-ivon

var pairs = new Array(length);
  for (var i = 0; i < length; i++) {
    pairs[i] = [keys[i], obj[keys[i]]];
}

 7. 數字0與-0的區別

// Identical objects are equal. `0 === -0`, but they aren't identical.
// See the [Harmony `egal` proposal](http://wiki.ecmascript.org/doku.php?id=harmony:egal).
if (a === b) return a !== 0 || 1 / a == 1 / b;
// 1/0 ===Infinity, 1/-0 === -Infinity