Array.prototype.map() 期望返回一个值，但不能根据其他问题返回 null，在箭头函数的末尾

Question

I am using the map function with an if statement that doesn't end in else. I have to be strict that only the defined recourseTypes are shown.

in eslint I get an error on my => as it doesn't end in an else

Array.prototype.map() expects a value to be returned at the end of arrow function.

Is there a correct way to write this?

Code:

   routes: async () => {
      const apiURL = process.env.BASE_URL
      const response = await axios.get(`${apiURL}/urls`)
      const { data: resources } = response.data
      const urlModule = resources.map((resource) => {
        const { resourceType } = resource

    if (resourceType === 'brand') {
      return {
        url: `/${resource.url}`,
        changefreq: 'weekly',
        priority: 0.9,
      }
    } else if (resourceType === 'product') {
      return {
        url: `/${resource.url}`,
        changefreq: 'monthly',
        priority: 0.8,
      }
    } else if (resourceType === 'category') {
      return {
        url: `/${resource.url}`,
        changefreq: 'weekly',
        priority: 0.7,
      }
    } else if (resourceType === 'document') {
      return {
        url: `/${resource.url}`,
        changefreq: 'weekly',
        priority: 0.6,
      }
    }
  })

  return [
    {
      url: '/',
      changefreq: 'daily',
      priority: 1,
    },
    {
      url: '/account',
      changefreq: 'daily',
      priority: 1,
    },
    {
      url: '/account/order-history',
      changefreq: 'daily',
      priority: 1,
    },
    ...urlModule,
  ]
},

Answer 1

You need to figure out a default to return in the else case. It doesn't technically need to be in an else block since you return in the other if blocks, it can just be at the end of the function. To ensure that only the allowed resourceType s are included, you can return some sort of output that you'll be able to recognize as an "error" if someone isn't using the right resourceType . You say you don't want to return null , presumably because you don't want that in the final array, so you could just return null and then filter with a simple .filter(item => item) to make sure everything is truthy, or you could explicitly check for null . Either way, you're going to have to return some sort of recognizable "error" default and handle that case.

Answer 2

Clarification : resources array contains all the resourceType that we are comparing using if/else clause ? As Array.map() will return the same number of elements as input array contains otherwise it will return with undefined.

Suggestion : Instead of multiple if/else-if clause, we can use multiple if statements for a better performance.

Demo :

 // Response coming from API. const resources = [{ resourceType: 'brand', url: 'brandUrl' }, { resourceType: 'product', url: 'productUrl' }, { resourceType: 'category', url: 'categoryUrl' }, { resourceType: 'document', url: 'documentUrl' }]; // Array of required ResourceTypes. const requiredResourceTypes = ['brand', 'product', 'document']; // Logic to filter and get the URL's object of the required resourceTypes. const urlModule = resources.filter(({resourceType}) => requiredResourceTypes.includes(resourceType)).map((resource) => { const { resourceType } = resource if (resourceType === 'brand') { return { url: `/${resource.url}`, changefreq: 'weekly', priority: 0.9, } } if (resourceType === 'product') { return { url: `/${resource.url}`, changefreq: 'monthly', priority: 0.8, } } if (resourceType === 'category') { return { url: `/${resource.url}`, changefreq: 'weekly', priority: 0.7, } } if (resourceType === 'document') { return { url: `/${resource.url}`, changefreq: 'weekly', priority: 0.6, } } }); console.log(urlModule);

Performance test result screenshot :