javascript - 如何使用字符串原型(prototype)的自定义创建方法？

Question

我创建了自己的方法，基本上将字符串中每个单词的第一个字母大写。

但是，我收到此 Uncaught TypeError: Cannot read property 'split' of undefined 错误。我哪里错了？

String.prototype.toCapitalize = (str) => {
  let splits = str.split(" ");
  let capitalize = '';
  splits.forEach((el) => {
    let result = el.charAt(0).toUpperCase() + el.substr(1, el.length).toLowerCase();
    capitalize = capitalize + ' ' + result;
  });
  return capitalize;
}
let h = 'its a beautiful weather';
h.toCapitalize();

Answer 1

你怎么认为第一个参数是字符串？它应该是 this。将 str 替换为 this 并有效:

String.prototype.toCapitalize = function () {
  let splits = this.split(" ");
  let capitalize = '';
  splits.forEach((el) => {
    let result = el.charAt(0).toUpperCase() + el.substr(1, el.length).toLowerCase();
    capitalize = capitalize + ' ' + result;
  });
  return capitalize;
}
let h = 'its a beautiful weather';
console.log(h.toCapitalize());