Why do the elements in my array show up as undefined?-CodePudding

I can't seem to figure out why I can't get the information out of the array

const usedPlatformLog: Date[] = []
users.forEach(el => {
    usedPlatformLog.push(el.lastUsed)
})
console.log(usedPlatformLog) // shows array with indexes 0 and 1 (picture attached)
console.log(usedPlatformLog[0]) // log response undefined

CodePudding user response：

undefined is a valid value, and can be pushed into arrays.

your array is [undefined, undefined] probably because users[0].lastUsed and users[1].lastUsed are also undefined. Maybe console.log(users) so you can actually see what's in that array.

CodePudding user response：

This may be happening because the lastUsed property of the el object is not defined or it is not of type Date.

In JavaScript, when you try to access a property of an object that is not defined or it is not of the expected type, it will return undefined.

To fix this issue, you can check if the lastUsed property exists and if it is of type Date before pushing it to the usedPlatformLog array.

Here is an example:

const usedPlatformLog: Date[] = []
users.forEach(el => {
   if (el.lastUsed && el.lastUsed instanceof Date) {
      usedPlatformLog.push(el.lastUsed)
   }
})

console.log(usedPlatformLog) // should now show the correct values in the array
console.log(usedPlatformLog[0]) // should now return the expected value