findIndex() always return -1 on array with objects

Question

I don't find the solution on following problem. The index keeps returning -1 instead of 1 in this case.

Anyone that can help me out?

let allRules = [{ruleName: "a"}, {ruleName: "b"}, {ruleName: "c"}]
let name = "b"
let index = allRules.findIndex(x => {
  console.log(x.ruleName)
  x.ruleName === name
})
console.log(index)

This a a great article to understand when you need to use brackets or return to your arrow functions https://codeburst.io/javascript-understand-arrow-function-syntax-ab4081bba85b — lampropoi, Nov 21 '19 at 12:45

score 2 · Accepted Answer · answered Nov 21 '19 at 12:40

You need to use return keyword as you have {} in your callback method:

let allRules = [{ruleName: "a"}, {ruleName: "b"}, {ruleName: "c"}]
let name = "b"
let index = allRules.findIndex(x => {
  console.log(x.ruleName)
  return x.ruleName == name
})
console.log(index)

An example without return statement:

let allRules = [{ruleName: "a"}, {ruleName: "b"}, {ruleName: "c"}]
let name = "b"
let index = allRules.findIndex(x => x.ruleName == name)
console.log(index)

score 1 · Answer 2 · answered Nov 21 '19 at 12:40

1

You need to add return.

let allRules = [{ruleName: "a"}, {ruleName: "b"}, {ruleName: "c"}]
let name = "b"
let index = allRules.findIndex(x => {
  console.log(x.ruleName)
  return x.ruleName === name
})
console.log(index)

answered Nov 21 '19 at 12:40

Afia

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score 1 · Answer 3 · answered Nov 21 '19 at 12:41

As @Nick Parsons in comments said you need to return something.

let allRules = [{ruleName: "a"}, {ruleName: "b"}, {ruleName: "c"}]
let name = "b"
let index = allRules.findIndex(x => {
  console.log(x.ruleName);
  return x.ruleName === name;
})
console.log(index)

findIndex() always return -1 on array with objects

3 Answers3