TypeError: string is not a function when Array.findIdex is used

October 19, 2024

Not sure if I’m doing an error in the code, but when I try to find the index of the letter z that is in the array I’ve split I will get this error:

TypeError: string "z" is not a function
    at Array.findIndex (<anonymous>)

Here is the code:

const chars: string = "abcdefghilmnopqrstuwxyz0123456789@-_+*(),.#";
let outputMatrix: Array<string> = [];
let outputWord: string = "";

// Split input matrix function 
const splitMatrix = async (inputMatrix: string) => {
  let splitted = inputMatrix.split(''); 
  let uppercaseChars = splitted.findIndex('z');
  console.log(uppercaseChars)
  console.log(splitted)
  return splitted;
}

// Generating random word
const createRandomString = (splittedChars: Array<string>, length?: number) => {
  const defaultLength: number = 12;
  const min: number  = 0;
  const max: number = splittedChars.length;
  let num: number;

  if (length) {
    for(let i: number = 0; i < length; i++) {
      num = Math.floor(Math.random() * (max - min) + min);
      outputWord += splittedChars[num];
    }
    return outputWord;
  } else {
    for(let i: number = 0; i < defaultLength; i++) {
      num = Math.floor(Math.random() * (max - min) + min);
      outputWord += splittedChars[num];
    }
  }
  console.log('Generated password', outputWord);
}

const main = () => {
  splitMatrix(chars)
    .then( (outputMatrix) => {
      createRandomString(outputMatrix);
    });
}

main();

What I want to do is to get the index of the z letter and after this extract all the elements that are before the letter including the letter to uppercase them.

>Solution :

The error occurs because you are passing a string (‘z’) directly into the findIndex method, which expects a function as its argument. The findIndex method requires a callback function that tests each element of the array to determine if it matches your criteria

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex

    const chars: string = "abcdefghilmnopqrstuwxyz0123456789@-_+*(),.#";
    let outputMatrix: Array<string> = [];
    let outputWord: string = "";
    
    // Split input matrix function 
    const splitMatrix = async (inputMatrix: string) => {
      let splitted = inputMatrix.split(''); 
      // Find the index of the letter 'z' correctly using a callback function
      let uppercaseChars = splitted.findIndex((char) => char === 'z');
      
      console.log(uppercaseChars);
      console.log(splitted);
      return splitted;
    }
    
    // Generating random word
    const createRandomString = (splittedChars: Array<string>, length?: number) => {
      const defaultLength: number = 12;
      const min: number  = 0;
      const max: number = splittedChars.length;
      let num: number;
    
      if (length) {
        for(let i: number = 0; i < length; i++) {
          num = Math.floor(Math.random() * (max - min) + min);
          outputWord += splittedChars[num];
        }
        return outputWord;
      } else {
        for(let i: number = 0; i < defaultLength; i++) {
          num = Math.floor(Math.random() * (max - min) + min);
          outputWord += splittedChars[num];
        }
      }
      console.log('Generated password', outputWord);
    }
    
    const main = () => {
      splitMatrix(chars)
        .then((outputMatrix) => {
          createRandomString(outputMatrix);
        });
    }
    
    main();