Step by Step solution about How to resolve the algorithm Determine if a string is collapsible step by step in the JavaScript programming language

The provided JavaScript code defines a method called collapse() that extends the String prototype, enabling strings to collapse consecutive duplicate characters into a single instance. Here's a detailed breakdown of the code:

1. Extending the String Prototype:

String.prototype.collapse = function() {

This code adds a new method named collapse() to the String prototype. This means that any string object can now call the collapse() method to perform the collapsing operation.

2. Iterating Over Characters:

 let str = this;
 for (let i = 0; i < str.length; i++) {

The code starts by assigning the current string to the str variable and initializes a loop that iterates over each character in the string. The loop uses an index i to traverse the characters.

3. Collapsing Consecutive Duplicates:

   while (str[i] == str[i+1]) str = str.substr(0,i) + str.substr(i+1);

Inside the loop, there's a nested while loop that checks if the current character (str[i]) is the same as the next character (str[i+1]). If consecutive duplicates are found, the code enters the inner loop.

Within the inner loop, the str variable is reassigned to a new string that consists of the substring before the current position (substr(0,i)) and the substring after the duplicate character (substr(i+1)). This effectively removes the consecutive duplicate characters.

4. Returning the Collapsed String:

 return str;
};

After iterating over all the characters and collapsing consecutive duplicates, the modified str variable, which now contains the collapsed string, is returned.

Testing the Collapse Function:

The code includes a section for testing the collapse() function. It provides an array of input strings (strings) and iterates over them:

// testing
let strings = [
 '',
 '"If I were two-faced, would I be wearing this one?" --- Abraham Lincoln ',
 '..1111111111111111111111111111111111111111111111111111111111111117777888',
 `I never give 'em hell, I just tell the truth, and they think it's hell. `,
 '                                                    --- Harry S Truman  '
];

For each input string, it calls the collapse() method and prints the original string along with its length, followed by the collapsed string and its length.

This extended collapse() method provides a convenient way to remove consecutive duplicate characters from any string, making it useful for tasks like data cleaning, text processing, or string manipulation in general.

String.prototype.collapse = function() {
  let str = this;
  for (let i = 0; i < str.length; i++) {
    while (str[i] == str[i+1]) str = str.substr(0,i) + str.substr(i+1);
  }
  return str;
}

// testing
let strings = [
  '',
  '"If I were two-faced, would I be wearing this one?" --- Abraham Lincoln ',
  '..1111111111111111111111111111111111111111111111111111111111111117777888',
  `I never give 'em hell, I just tell the truth, and they think it's hell. `,
  '                                                    --- Harry S Truman  '
];
for (let i = 0; i < strings.length; i++) {
  let str = strings[i], col = str.collapse();
  console.log(`«««${str}»»» (${str.length})`);
  console.log(`«««${col}»»» (${col.length})`);
}