JavaScript 5 新增 Array 方法实现介绍

/*! 
* jLip JavaScript Library v0.1 
* 
* Copyright 2012, Lip2up ([e-mail]) 
* Just for free use, NO LICENSE 
*/ 
(function() { 
function extend(target, props) { 
for (var m in props) { 
if (target[m] === undefined) target[m] = props[m]; 
} 
} 
var fns = { every: 1, some: 2, forEach: 3, map: 4, filter: 5 }, 
reduceError = 'Reduce of empty array with no initial value'; 
function each(fn, _this, kind) { 
var len = this.length, ret = kind == fns.filter ? [] 
: kind == fns.map ? Array(len) : undefined, 
find = kind == fns.some, i, v; 
for (i = 0; i < len; i++) { 
if (this[i] !== undefined) { 
v = fn.call(_this, this[i], i, this); 
switch (kind) { 
case fns.every: 
case fns.some: 
if (v === find) return find; 
break; 
case fns.map: 
ret[i] = v; 
break; 
case fns.filter: 
if (v === true) ret[ret.length] = this[i]; 
break; 
} 
} 
} 
return kind >= fns.forEach ? ret : !find; 
} 
function reduce(fn, init, right) { 
var len = this.length, i, prev, inc = right ? -1 : 1; 
if (len == 0 && init === undefined) 
throw TypeError(reduceError); 
for (i = right ? len - 1 : 0, prev = init; 
prev === undefined && (right ? i >= 0 : i < len); 
i += inc) { 
prev = this[i]; 
} 
if (prev === undefined && i == (right ? -1 : len)) 
throw TypeError(reduceError); 
for (; (right ? i >= 0 : i < len); i += inc) { 
if (this[i] !== undefined) 
prev = fn(prev, this[i], i, this); 
} 
return prev; 
} 
extend(Array.prototype, { 
every: function(fn, _this) { 
return each.call(this, fn, _this, fns.every); 
}, 
some: function(fn, _this) { 
return each.call(this, fn, _this, fns.some); 
}, 
forEach: function(fn, _this) { 
return each.call(this, fn, _this, fns.forEach); 
}, 
map: function(fn, _this) { 
return each.call(this, fn, _this, fns.map); 
}, 
filter: function(fn, _this) { 
return each.call(this, fn, _this, fns.filter); 
}, 
reduce: function(fn, init) { 
return reduce.call(this, fn, init); 
}, 
reduceRight: function(fn, init) { 
return reduce.call(this, fn, init, true); 
} 
}); 
})();