javascript - 自增运算符返回 NaN

Question

我正在尝试使用 ++ 运算符递增一个变量，但我一直得到 NaN 结果，我不确定为什么。这是我的代码:

var wordCounts = { };
var x = 0
var compare = "groove is in the heart";
        var words = compare.split(/\b/);
        for(var i = 1; i < words.length; i++){
            if(words[i].length > 2){
                wordCounts["_" + words[i]]++;
            }
        }


alert(wordCounts.toSource());

Answer 1

wordCounts["_"+ words[i]] 的值最初是 undefined 所以当你++ 它时，它给你 NaN。只需将您的代码更改为:

if (wordCounts["_" + words[i]]) {
    wordCounts["_" + words[i]]++;
} else {
    wordCounts["_" + words[i]] = 1;
}