# forEach方法模型
[pre]    function forEach(array, action) {
for (let i = 0; i < array.length; i++) {
action(array);
}
}[/pre]# filter方法模型
[pre]    function filter(array, test) {
var passed = [];
for (let i = 0; i < array.length; i++) {
if (test(array))
passed.push(array);
}
}[/pre]filter方法需要return
# map 方法模型
[pre]    function map(array, transform) {
var mapped = [];
for (var i = 0; i < array.length; i++)
mapped.push(transform(array));
return mapped;
}[/pre]map方法需要return
# reduce方法模型
[pre]    function reduce(array, combine, start) {
var current = start;
for (var i = 0; i < array.length; i++)
current = combine(current, array);
return current;
}[/pre]