The x.name and imgname have the same type (string) and the same value "cardpro_capsule_model_2". But why the findIndex() function return -1? Please explain it to me.

findPicture(imgname): number {
   return this.infocardList.findIndex(x => {
      x.name === imgname;          // result in console:
      console.log(imgname)         // cardpro_capsule_model_2
      console.log(typeof imgname)  // string
      console.log(typeof x.name)   // string
      console.log(x.name);         // cardpro_capsule_model_2
   })
  }

Expect result will be index of the element in array not -1.

The x.name and imgname have the same type (string) and the same value "cardpro_capsule_model_2". But why the findIndex() function return -1? Please explain it to me.

findPicture(imgname): number {
   return this.info.cardList.findIndex(x => {
      x.name === imgname;          // result in console:
      console.log(imgname)         // cardpro_capsule_model_2
      console.log(typeof imgname)  // string
      console.log(typeof x.name)   // string
      console.log(x.name);         // cardpro_capsule_model_2
   })
  }

Expect result will be index of the element in array not -1.

• javascript
• arrays

Share Improve this question Follow edited Oct 16, 2019 at 14:19 CollinD 7,58322 gold badges2424 silver badges4747 bronze badges asked Oct 16, 2019 at 13:55 Tùng BillTùng Bill 14911 gold badge33 silver badges1414 bronze badges 2

• 2 you need add a return statement – juancarlos Commented Oct 16, 2019 at 13:58
• 1 Because you're NOT returning the result of the parison. That's all that's going on here. – Dženis H. Commented Oct 16, 2019 at 14:11

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3 Answers 3

Sorted by: Reset to default 5

Your findIndex callback always returns undefined, you should instead return x.name === imgname;

The findIndex function essentially does something like

if (findIndexCallback(element)) return index;

for each element of the array. So if your function returns nothing (undefined), the fallback value of -1 meaning "not found" is returned.

See https://developer.mozilla/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex for full documentation.

you need add a return statement on your findIndex

findPicture(imgname): number {
  return this.info.cardList.findIndex(x => {
     return x.name === imgname;          // result in console:
  })

}

You need to return the result from your findIndex function.

findPicture(imgname): number {
    return this.info.cardList.findIndex(x => {
    return x.name === imgname;
    });
 }