我有一个包含图像和文档的对象数组，我想检查 mime_type 并选择要显示的第一个元素（React）<img> 标签

Question

I have a array of objects which contain images and documents, I want to check is the mime_type is 'images/jpeg' or 'image/png' and then only display the first image in a tag. I am using react.

I tried this but I keep getting undefined

<img className={"img-fluid img-list"} 
   src={this.state.images.filter(img => (img.mime_type === 'image/jpeg' || img.mime_type === 'image/png') || {})[0].blob_url} 
   alt="" />


<img className={"img-fluid img-list"} 
   src={this.state.images.filter(img => (img.mime_type === 'image/jpeg' || img.mime_type === 'image/png'))[0].blob_url} 
   alt="" />

if check with a {} i dont get any links

any help much appriciated.

Answer 1

You have an error here:

this.state.images.filter(img => (img.mime_type === 'image/jpeg' || img.mime_type === 'image/png') || {})[0].blob_url

It should be:

((this.state.images.filter(img => (img.mime_type === 'image/jpeg' || img.mime_type === 'image/png')) || [])[0] || {}).blob_url

If you add a bit of indentation, it should be more clear where your error was:

(
  (
    this.state.images.filter(img => (
      img.mime_type === 'image/jpeg' || img.mime_type === 'image/png'
    ))     // give me an array with only the images
    || []  // OR give me back an empty array if you cannot find any
  )[0]     // then give me the first element (image object) of the array
  || {}    // OR give me back an empty object if the array is empty
).blob_url // finally give me the `blobl_url` of the object

Alternatively, you can use Array.prototype.find , which will return the first item matching the criteria:

(this.state.images.find(img => (img.mime_type === 'image/jpeg' || img.mime_type === 'image/png')) || {}).blob_url