计算数组中每一个元素出现的次数

方法一：使用数组的归并方法reduce()
var names = ['China', 'Peter', 'Bob', 'Peter', 'China'];
var countedNames = names.reduce(function (allNames, name) {
if (name in allNames) {
allNames[name]++;
}
else {
allNames[name] = 1;
}
return allNames;
}, {});