javascript - JS toLowerCase() 不工作

Question

我有这段代码:

//make first letter of each word capital
function titleCase(str) {
    /*
     *  1. change all letters to lower case
     *  2. split words
     *  3. set each 1st letter to Capital
     *  4. combine array back into string
     */
    arr = [];
    str.toLowerCase();

    arr = str.split(" ");

    for (var index = 0; index < arr.length; index++) {
        arr[index].charAt(0).toUpperCase();
    }

    str= arr.join(" ");
    return str;
}
console.log(titleCase("Potato potato potato"));

而且我不明白为什么 toLowerCase() 和 toUpperCase() 不起作用。我做错了什么？

Answer 1

需要2个更新

1. 将 str.toLowerCase() 重新分配给 str
2. 将更新的数组值重新分配回数组。

请注意，除非您重新分配值，否则原始值不会更改。因此，结果没有受到影响。

//make first letter of each word capital
function titleCase(str) {
/*
1. change all letters to lower case
2. split words
3. set each 1st letter to Capital
4. combine array back into string
*/
    arr = [];
    str = str.toLowerCase(); // **** Problem 1 - Reassigning

    arr = str.split(" ");

    for (var index = 0; index < arr.length; index++) {
       // **** Problem 2 - Reassigning
       arr[index] = arr[index].charAt(0).toUpperCase() + arr[index].slice(1);
    }

    str= arr.join(" ");
    return str;
}
console.log(titleCase("Potato potato potato"));