Taken from Execute Program

Use .findIndex to write the function find(arr, callback). It should return the first element where callback(element) is true. If the element is not found, it should return undefined.

Solution

This is the answer I came up with:

// typescript

function find(arr: Array<any>, callback: any) {
  let index = arr.findIndex(callback)
  return ( index >= 0 ) ? arr[index] : undefined
}

Testing

Solution tested in REPL:

https://www.typescriptlang.org/play?#code/GYVwdgxgLglg9mABMGYAmAKAhgJxwLkQEE8sBPAHizDID4AaRCLAGxYCMsIBrQ6sgJSIA3gFgAUIkQsAplESo0MgB6IAvIlw4AdCnQBJdCozM2nHgIlScckDiQYFR1bQ0AGREID8mvAG1FFQBdREJwJT0ZNAkAXwkJCAQAZzhZbRY4AHMMKylkRQw-AEZGACZGAGYgxgwwQjAQAFt2GRwhNVpEJDUexCKBRgB6Qb7cqT1MPwBWRgA2RgB2asRa+qaWtvVOpBHS9V6KgcRhxFmx-PRCksRyxCqauq711vbtxE6po5PwmUjoyTyE0Ky1WT2aLy2XXeiE+QxGPz+5yBfgabBBj34ryhPQ0qJYXxGeIklnECWS8i06kQxTKQQkWj8AFoiiENBUyWAUmkMtkkQUtA81uDNh1sb1Ycd4UZEeISUA