使用箭头函数中的for循环将数组中的第一个字符大写

Question

目标是使数组中各项的首字母大写，但未打印出来

const words = ["planes", "trains", "automobiles"];
const singularWords = words.map(w => w.slice(0, -1))
// The below line should console.log: ["plane", "train", "automobile"]
console.log(singularWords);

// Bonus:
const capitalizedWords = words.map((w) => {
  for (let i = 0; i < words.length; i++) {
    words[i] = words[i].charAt(0).toUpperCase();
  }
});
// The below line should console.log: ["Planes", "Trains", "Automobiles"]
console.log(capitalizedWords);

Answer 1

您映射并循环

只需映射，然后再次使用切片

PS：a discussion of w[0] vs w.charAt(0)

const words = ["planes", "trains", "automobiles"];
const singularWords = words.map(w => w.slice(0, -1))
// The below line should console.log: ["plane", "train", "automobile"]
console.log(singularWords);

// Bonus:
const capitalizedWords = words.map(w => w.charAt(0).toUpperCase()+w.slice(1));
// The below line should console.log: ["Planes", "Trains", "Automobiles"]
console.log(capitalizedWords);

Answer 2

该功能-map()基本上在为您循环。

const words = ["planes", "trains", "automobiles"];
const singularWords = words.map(w => w.slice(0,-1))
// The below line should console.log: ["plane", "train", "automobile"]
console.log(singularWords);

// Bonus:
const capitalizedWords = words.map((w) => {
  return w.charAt(0).toUpperCase() + w.slice(1);
});
// The below line should console.log: ["Planes", "Trains", "Automobiles"]
console.log(capitalizedWords);

这里是正确的代码。

希望这会有所帮助！

Answer 3

const words = ["planes", "trains", "automobiles"];
const singularWords = words.map(w => w.slice(0, -1))
// The below line should console.log: ["plane", "train", "automobile"]
console.log(singularWords);

// Bonus:
const capitalizedWords = words.map(w => w[0].toUpperCase()+w.slice(1));
// The below line should console.log: ["Planes", "Trains", "Automobiles"]
console.log(capitalizedWords);

仅使用地图。您可以dele charAt，并添加w [0]

Answer 4

这更多是表示使用解构模式的替代方法。

想法

• 在箭头功能中，对第一个参数使用解构模式
• 具有2个变量：
  • firstChar：保留第一个字符，这将用于大写。
  • rest：其余字符。但是，由于我们使用的是散布运算符，因此它将是一个数组，因此必须使用.join('')。

const words = ["planes", "trains", "automobiles"];
const singularWords = words.map(([ firstChar ]) => firstChar )
// The below line should console.log: ["plane", "train", "automobile"]
console.log(singularWords);

// Bonus:
const capitalizedWords = words.map(( [ firstChar, ...rest ] ) => firstChar.toUpperCase() + rest.join('') );
// The below line should console.log: ["Planes", "Trains", "Automobiles"]
console.log(capitalizedWords);