<!DOCTYPE HTML>
<html>
<body>
</body>
<script type="text/javascript">
(function(root) {
var push = Array.prototype.push;
var _ = function(obj) {
if (obj instanceof _) {
return obj;
}
if (!(this instanceof _)) {
return new _(obj);
}
this._wrapped = obj;
}
var cb = function(iteratee, context, count) {
if (iteratee == null) {
return _.identity;
}
if (_.isFunction(iteratee)) {
return optimizeCb(iteratee, context, count);
}
}
//optimizeCb优化迭代器
var optimizeCb = function(func, context, count) {
if (context == void 0) {
return func;
}
switch (count == null ? 3 : count) {
case 1:
return function(value) {
return func.call(context, value);
};
case 3:
return function(value, index, obj) {
return func.call(context, value, index, obj);
};
case 4:
return function(memo, value, index, obj) {
return func.call(context, memo, value, index, obj);
};
}
}
_.isArray = function(array) {
return toString.call(array) === "[object Array]";
}
_.each = function(target, callback) {
var key, i = 0;
if (_.isArray(target)) {
var length = target.length;
for (; i < length; i++) {
callback.call(target, target[i], i);
}
} else {
for (key in target) {
callback.call(target, key, target[key]);
}
}
}
_.each(["Function", "String", "Object", "Number", "Boolean", "Arguments"], function(name) {
_["is" + name] = function(obj) {
return toString.call(obj) === "[object " + name + "]";
}
});
//predicate 真值检测(重点: 返回值)
_.filter = function(obj, predicate, context) {
var results = [];
predicate = cb(predicate, context);
_.each(obj, function(value, index, list) {
if (predicate(value, index, list)) results.push(value);
});
return results;
};
root._ = _;
})(this);
/*思路：定义一个underscore的filter函数，因为只有NaN是不等于自身的，所以真值检测中设置返回等于自身的元素
*/
var arr = [NaN ,1,21,32,NaN,41,5];
var bb = _.filter(arr,function(num) {
return num === num;
});
console.log(bb);//[1, 21, 32, 41, 5]
</script>
</html>
转载于:https://www.cnblogs.com/yina-526/p/11315548.html
