javascript - 获取单词中重复次数最多的字母

Question

我想统计一个单词中出现次数最多的字母

function GreatestCount(str)
{
    var count = {}

    for (var i = 0 ; i<str.length;i++)
    {
        var char = str[i];
        count[char] = (count[char] || 0) + 1;

    }

     //get the largest number for the letter counts
    var max = 0;

    for (var c in count) {
        if (count[c] > max) max = count[c];
    }

    return max
}

谁能告诉我为什么

count[char] = (count[char] || 0) + 1;// this works

count[char] += 1 // this does not work 

Answer 1

因为

count[char] += 1

等于

count[char] = count[char] + 1

并且第一次运行代码时，count[char] 是undefined 所以它几乎与

undefined + 1 // which is NaN

工作版本通过使用 || 运算符安全地添加 0 来规避这种情况。