Basic Alogrithm Scripting Challenges [TitleCase]

1

Hi guys, could someone please explain how this code is working?

String.prototype.replaceAt = function(index, character) {
    return this.substr(0, index) + character + this.substr(index+character.length);
};


function titleCase(str) {
    var newTitle = str.split(' ');
    var updatedTitle = [];
    for (var st in newTitle) {
        updatedTitle[st] = newTitle[st].toLowerCase().replaceAt(0, newTitle[st].charAt(0).toUpperCase());
    }
    return updatedTitle.join(' ');
}

titleCase("I'm a little tea pot");

Specifically, what exactly is happening when something is passed to replaceAt? What exactly is passed to it, and what does replaceAt do with it? Specifically this line: this.substr(0, index) + character + this.substr(index+character.length). I don’t get heads or tails of what that line is doing, what it’s adding, and what the end product is that it’s returning.

2

The code extends builtin String by adding replaceAt to its prototype - then replaceAt can be used in a chain of function calls

The this reference in replaceAt is to the string object on which the function is called - the function extracts two pieces of the string - the initial part up to just before index and the trailing part from index+character.length onward - it pastes the two pieces together with character in between and returns the new string

Effectively replaceAt replaces a portion of a string starting at a given index with another string

1 Like