JSFiddle - React, Tailwind, and code Playground

JavaScript

/* Creates mechanism that finds a word in a paragraph and replaces it
   with another word */

//Declare the original string
var paragraph = "The quick brown fox jumps over the lazy dog";

//Convert paragraph in individual words
var tempArray = paragraph.split(" "); 

// Introduce the word to be found; to be replaced
var oldWord = "brown";

// Introduces new word to replace old
var newWord = "red";

//Iterate over the array to find and replace the word
for (var i = 0; i < tempArray.length; i++) {
    if (tempArray[i] === oldWord) {
        tempArray[i] = newWord;
    }
}

/* Reconvert the modified array to string by assigning it to the
   original variable */

paragraph = tempArray.join(" ");

// Display your results, it's not an array anymore
console.log(paragraph);