Changing individual characters in a string does not work in a loop

Question

So, I'm working on some exercise questions. My code seems to be working fine up until I decide to loop through the string to replace any instance of a period with nothing. For some reason, the loop doesn't work. I imagine it has something to do with not calling it somehow, but I'm not sure how to call the loop. I thought that loops automatically overwrote what they are looping through. Here is the exercise and my incomplete solution:

Write a JavaScript function to parameterize a string.

function string_parameterize(string) {
    var lowercase_string = string.toLowerCase();
    var split_string = lowercase_string.split(" ");
    var joined_string = split_string.join("-");
    for (i = 0; i < joined_string.length; i++) {
        if (joined_string[i] === ".") {
            joined_string[i] === "";
        }
    }
    return joined_string;
}

//Test Data :
console.log(string_parameterize("Robin Singh from USA."));

The answer should be robin-singh-from-usa without the period, but it keeps coming out as robin-singh-from-usa. with the period.

Answer 1

The other answers are not taking into account that strings in JavaScript are immutable. You can not change individual characters in a string. You build a new string.

In JavaScript, strings are immutable. Trying to change the characters in a string does not work:

function string_parameterize(string) {
    var lowercase_string = string.toLowerCase();
    var split_string = lowercase_string.split(" ");
    var joined_string = split_string.join("-");
    for (i = 0; i < joined_string.length; i++) {
        if (joined_string[i] === ".") {
            joined_string[i] = "";
        }
    }
    return joined_string;
}

//Test Data :    
console.log(string_parameterize("Robin Singh from USA.")); //This will not work:

You can build a new string using your for loop to individually add each character that is not a . to the newString:

function string_parameterize(string) {
    var lowercase_string = string.toLowerCase();
    var split_string = lowercase_string.split(" ");
    var joined_string = split_string.join("-");
    var newString = '';
    for (i = 0; i < joined_string.length; i++) {
        if (joined_string[i] !== ".") {
            newString += joined_string[i];
        } //We are replacing '.' with nothing, '', so no need for an else
    }
    return newString;
}

//Test Data :
console.log(string_parameterize("Robin Singh from USA."));

Regular Expressions

This would, however, normally be done with Regular Expressions, specifically the .replace() method:

function string_parameterize(string) {
    var lowercase_string = string.toLowerCase();
    var newString = lowercase_string.replace(/ /g,'-'); //Replace all spaces with '-'.
    var newString = newString.replace(/\./g,''); //Replace all '.' with nothing. The '.'
                                                 //  has to be quoted with \. as it
                                                 //  has special meaning in a RegExp.     
    return newString;
}
//Test Data :
console.log(string_parameterize("Robin Singh from USA."));

Which can be done all in one statement:

function string_parameterize(string) {
    return string.toLowerCase().replace(/ /g,'-').replace(/\./g,'');
}
//Test Data :
console.log(string_parameterize("Robin Singh from USA."));

Answer 2

You can put in a [...]+ every character you don't want have in the output.

var res = string.toLowerCase().replace(/[%\(\)\.\s]+/g, "-").replace(/-$/, "");
                                      // ^ ^ ^   ^
                                      // Here the characters you don't want to have in the output

+ means matched one ore more times. Replace the matched characters with -.

Then remove last - with -$.

In total

function string_parameterize(string) {
  var res = string.toLowerCase().replace(/[%\(\)\.\s]+/g, "-").replace(/-$/, "");
  return res;
}

console.log(string_parameterize("Это тест")); // A russian sentence
console.log(string_parameterize("Robin Singh%%() from USA.   "));
console.log(string_parameterize("Robin ...Singh    from USA....."));
console.log(string_parameterize("Robin Singh    from USA    "));
console.log(string_parameterize("Robin Singh    from USA"));

Info about regular expression.

Answer 3

function string_parameterize(str){
    return str.toLowerCase().replace(".", "").split(" ").join("-");
}
console.log(string_parameterize("Robin Singh from USA."));
//will result in: robin-singh-from-usa

Your code is not working because in if condition you are checking for joined_string[i]==="." to be equal to '.' and actually it is equal to 'USA.'. That is why this if condition never met with and return the '.' in the final result:

if (joined_string[i]===".") {
    joined_string[i]==="";
}

Answer 4

function string_parameterize(string) {
    var lowercase_string = string.toLowerCase();
    var split_string = lowercase_string.split(" ");
    var joined_string = split_string.join("-");
    joined_string = joined_string.replace(".", "");
    return joined_string;
}

//Test Data :
console.log(string_parameterize("Robin Singh from USA."));

This is working in IE.

Answer 5

You're checking the value of joined_string[i], rather than assigning it.

joined_string[i] = "";

not

joined_string[i] === "";

Answer 6

Change:
if (joined_string[i]===".") {
            joined_string[i]==="";
        }
to 

if (joined_string[i]===".") {
            joined_string[i]="";
        }