In javascript, how to insert a letter (eg: T) right before all the capital and lowercase F's in a word?

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I am trying to solve a problem in JavaScript. I have a string text consisting of English word. I need to find all the capital and lowercase F's in a word and need to insert T in front of that word. Please help me! Thank you.

What I have tried:

function addTbeforeFs(text, chr) {
  var output = '';
  for (var i = 0; i < text.length; i++) {
    if (i % 3 === 0) output += chr;
    output += text.charAt(i);
  }

  return output;
}

alert(addTbeforeFs('Fluffy', 'T'));

//My Output is : TFluTffy

// Expected Output should be: TFluTfTfy

Posted 26-Mar-20 7:20am

Member 14783910

Updated 26-Mar-20 7:39am

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phil.o 26-Mar-20 13:23pm

Why do you insert chr every three characters instead of testing for the current value and act accordingly? i % 3 === 0 will not test whether current letter is an upper or lower-case F.

Member 14783910 26-Mar-20 13:31pm

I am new to JS, i am trying to figure it out how to get the expected output... I am thinking to apply RegExp but don't know where to start... and yes what i did over there may be it is the wrong way to approach the solution. Thank you!

phil.o 26-Mar-20 14:01pm

You should try to do it without a regular expression first; you should learn to do it the iterative way, because that's the point of the exercise: iterate a string, test for a given condition, and act accordingly.
Begin by drawing a diagram on a piece of paper, then translate that into code.

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Richard Deeming · Answer 1 · 2020-03-26T07:41:00

Solution 1

Regular expressions would be the easiest option:

JavaScript

function addLetterBeforeFs(text, letterToAdd) {
    return text.replace(/f/gi, letterToAdd + "$&");
}

Regular expressions - JavaScript | MDN[^]
String.prototype.replace() - JavaScript | MDN[^]

Posted 26-Mar-20 7:41am

Richard Deeming