Property length does not exist on type string | number

Here is the type of the variable

type imageTags: string | number | {
    tag_type: string;
    tag_name: string;
    tag_id: number;
    photo_id: number;
    confidence: number;
}[]

This is how i try to access its properties.

    if (imageTags.length > 0) {
      return imageTags[0].tag_name === image_type;
    }

The variable can be a string , number or array then why am I getting the error Property 'length' does not exist on type 'string | number | { tag_type: string; tag_name: string; tag_id: number; photo_id: number; confidence: number; }[]'. Property 'length' does not exist on type 'number'.ts(2339)

CodePudding user response：

imageTags is declared as either string, number, or an array of objects. Maybe you expected it to be an array of string, number and/or objects instead, so that it's always an array? Then you should use parentheses:

type imageTags: (string | number | {
    tag_type: string;
    tag_name: string;
    tag_id: number;
    photo_id: number;
    confidence: number;
})[]

CodePudding user response：

You could check if imageTags's type is Array and only then check the length:

if (Array.isArray(imageTags) && imageTags.length) {
  return imageTags[0].tag_name === image_type;
}