ut2/lib/countBy.js

一个现代 JavaScript 实用工具库。[点击查看在线文档]。

'use strict';

var forEach = require('./forEach.js');
var createIteratee = require('./internals/createIteratee.js');

var countBy = function (collection, iteratee) {
    var result = {};
    var internalIteratee = createIteratee(iteratee);
    forEach(collection, function (item, index, arr) {
        var key = internalIteratee(item, index, arr);
        if (key in result) {
            ++result[key];
        }
        else {
            result[key] = 1;
        }
    });
    return result;
};

module.exports = countBy;