Introduction to the implementation of the new Array method in JavaScript 5_javascript skills

复制代码 代码如下:

/*!
* jLip JavaScript Library v0.1
*
* Copyright 2012, Lip2up (lip2up@qq.com)
* 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);
}
});
})();