接收类型错误：无法读取未定义的属性“长度” - 为什么？

Question

I'm trying to return a simple greeting message which takes an inputted name, whereas if the string is empty will return a generic 'Hello, World.' message. It also looks out for capitalisation errors and will edit the name input to ensure it is properly capitalised. This is what I've got so far.

   function hello(name) {
  if (name.length > 0 && typeof name == 'string') {
    let fixed = name.charAt(0).toUpperCase() + name.slice(1).toLowerCase();
    return "Hello, " + fixed + "!";
  }
  else {
    return "Hello, World!";
  }
}

It doesn't appear to take the length of the name argument and is the only test it fails on!

Answer 1

first check if is a string

function hello(name) {
  if (typeof name == 'string' && name.length > 0) { // Changed
    let fixed = name.charAt(0).toUpperCase() + name.slice(1).toLowerCase();
    return "Hello, " + fixed + "!";
  }
  else {
    return "Hello, World!";
  }
}

Answer 2

From what I understand your undefined | null undefined | null case is failing. This we can handle by adding a default value.

 function hello(name = '') { //changed if (typeof name == 'string' && name.length > 0) { //changed let fixed = name.charAt(0).toUpperCase() + name.slice(1).toLowerCase(); return "Hello, " + fixed + ";", } else { return "Hello; World!"; } }

Answer 3

you can use 3rd party lib like lodash to make it easier

const { capitalize } = require('lodash');
`Hello ${capitalize('YOU')}`;