Writing indexOf function in JavaScript

Question

I am new to JavaScript. I have created a indexof function in but it is not giving the correct output: Question is: /* Implement a function called indexOf that accepts two parameters: a string and a character, and returns the first index of character in the string. */

This is my code:

function indexOf(string, character) {
  let result = string;
  let i = 0;
  let output = 1;

  while (i < result.length) {
    if (result[i] === character) {
      output = output + indexOf[i];
    }
  }

  return output;
}

I want to know what i am doing wrong. Please Help.

Mark · Accepted Answer · 2019-04-27 22:20:53Z

You are making things a little harder than you need to. If you want to do this without calling the built-in indexOf(), which I assume is the point of the exercise, you just need to return from the function as soon as your condition matches. The instructions say "return the first index" — that's the i in your loop.

If you make it through the loop without finding something it's traditional to return -1:

function indexOf(string, character) {
    let i=0;
    while(i < string.length){
        if(string[i] == character){  // yes? just return the index i
            return i
        }
        i++                          // no? increase i and move on to next loop iteration
    }
    return -1;                       // made it through the loop and without returning. This means no match was found.
}
console.log(indexOf("Mark Was Here", "M"))
console.log(indexOf("Mark Was Here", "W"))
console.log(indexOf("Mark Was Here", "X"))

Geuis · Accepted Answer · 2019-04-27 22:26:22Z

0

Assuming from your question that the exercise is to only match the first occurrence of a character and not a substring (multiple characters in a row), then the most direct way to do it is the following:

const indexOf = (word, character) => {
  for (let i = 0; i < word.length; i++) {
    if (word[i] === character) {
      return i;
    }
  }

  return -1;
}

If you also need to match substrings, leave a comment on this answer if you can't figure it out and I'll help you along.

answered Apr 27, 2019 at 22:26

Geuis

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Comments

Cat_Enthusiast · Accepted Answer · 2019-04-27 22:09:56Z

0

indexOf() is a built in method for strings that tells you the index of a particular character in a word. Note that this will always return the index of the FIRST matching character.-

You can write something like:

function indexOf(string, character){
   return string.indexOf(character)
}

So if I were to use my function and pass in the two required arguments:

indexOf("woof", "o") //this would return 1

answered Apr 27, 2019 at 22:09

Cat_Enthusiast

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Comments

Remon Lawendi · Accepted Answer · 2023-05-11 04:47:39Z

0

This code can be instead of indexOf(), the first param for the word u wants to search in and the second param for the string u want to search with.

function insteadIndexOF(mainWord,checkerWord){
  let one = ''
  let two = ''
  for(let i = 0 ; i < checkerWord.length ; i++){
    one += mainWord[i]
    two += checkerWord[i]
  }
  if(one === two ){
    return 0
  }
  return -1
}

answered May 11, 2023 at 4:47

Remon Lawendi

1

Comments

Vijay Kolar · Accepted Answer · 2023-11-13 06:55:53Z

0

const arr = ["I", "study", "JavaScript"];

function indexOf(str){
  for (let i = 0; i< arr.length; i++) {
    if (str === arr[i]) {
      return i
    }
  }
  return -1;

}
console.log(indexOf("JavaScript"))

edited Nov 13, 2023 at 6:55

answered Nov 13, 2023 at 6:55

Vijay Kolar

11 bronze badge

1 Comment

BDL Over a year ago

This is almost the same code (except for array declaration and console output) as in stackoverflow.com/a/77472166

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