Develop Reference

Is it possible to replace only one character in a string if that character appears twice consecutively?

So I made a method to make the first letter of all the words in any string Uppercase.
String.prototype.toMyCase = function () {
let strArray = Array.from(this.split(" "));
for(let i=0; i<strArray.length; i++){
strArray[i] = strArray[i][0].toUpperCase() + strArray[i].substr(1);
}
let newStr = strArray.toString();
let finalStr = newStr.replace(/,/g, " ");
return finalStr;
};
The problem with this is when I pass a string that has real commas(,) it replace that comma(,) too in the finalStr step. For e.g
console.log("How can mirrors be real, if our eyes aren't real".toMyCase(); gives me
How Can Mirrors Be Real If Our Eyes Aren't Real (there are two spaces after Real).

You can use strArray.join(' ');
String.prototype.toMyCase = function () {
let strArray = Array.from(this.split(" "));
for(let i=0; i<strArray.length; i++){
strArray[i] = strArray[i][0].toUpperCase() + strArray[i].substr(1);
}
return strArray.join(' ');
};
console.log("How can mirrors be real, if our eyes aren't real".toMyCase());

How about with this single line soln after string split(), uppercase first character and join the rest using .map() with the first?,
let str = "How can mirrors be real, if our eyes aren't real";
let captialized_words = str => str.split(' ').map(w => w.substring(0, 1).toUpperCase() + w.substring(1)).join(' ')
console.log(captialized_words(str))

Instead of
let finalStr = newStr.replace(/,/g, " ");
Do
let finalStr = newStr.replace(/,/g, "");

Split string on two delimiters?

I want to split a string based on the delimiters " " and "," (including quotation marks). How would I be able to do this? I tried doing this:
var str = '"String","String2" "String3"';
str = str.split('" "', '","');
console.log(str);
But it didn't work. I was expecting this console output:
["String", "String2", "String3"]
But I got:
[]
How do I split a string based on two delimiters? Is it possible?

let str = '"String","String2" "String3"';
str = str.split(/ |,/);
console.log(str);
let str2 = '"String","String2" "String3"';
str2 = str2.split(/" "|","|"|\n/).filter(Boolean);
console.log(str2);
let str3 = '"String","String2" "String3"';
str3 = str3.match(/[\w\d]+/g);
console.log(str3);

You can specify regex or array as delimiter
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split

try below solution
var str = '"String","String2" "String3"';
str = str.match(/\w+|"[^"]+"/g)
str = str.map(function(x){return x.replace(/"/g, '');});
console.log('Final str : ', str);

You can use regex: str = str.split(/,| /)
console.log("a,b c".split(/,| /));

How to get substring value from main string?

I have string similar to this one.
HTML
var str = "samplestring=:customerid and samplestring1=:dept";
JS
var parts = str.split(':');
var answer = parts;
I want to trim substrings which starts with colon: symbol from the main string
But it is returing the value like this
samplestring=,customerid and samplestring1=,dept
But I want it something like this.
customerid,dept
I am getting main string dynamically it may have colon more then 2.
I have created a fiddle also link

var str = "samplestring=:customerid and samplestring1=:dept";
alert(str.match(/:(\w+)/g).map(function(s){return s.substr(1)}).join(","))

you can try regex:
var matches = str.match(/=:(\w+)/g);
var answer = [];
if(matches){
matches.forEach(function(s){
answer.push(s.substr(2));
});
}

Here's a one-liner:
$.map(str.match(/:(\w+)/g), function(e, v) { return e.substr(1); }).join(",")

Try
var str = "samplestring=:customerid and samplestring1=:dept";
var parts = str.split(':');
var dept = parts[2];
var cus_id = parts[1].split(' and ')[0];
alert(cus_id + ", " + dept );
Using this you will get o/p like :customerid,dept

this will give you what you need...
var str = "samplestring=:customerid and samplestring1=:dept";
var parts = str.split(' and ');
var answer = [];
for (var i = 0; i < parts.length; i++) {
answer.push(parts[i].substring(parts[i].indexOf(':')+1));
}
alert(answer);

var str = "samplestring=:customerid and samplestring1=:dept";
alert(str.replace(/[^:]*:(\w+)/g, ",$1").substr(1))

You can try it like this
var str = "samplestring=:customerid and samplestring1=:dept and samplestring11=:dept";
var results = [];
var parts = str.split(' and ');
$.each(parts, function( key, value ) {
results.push(value.split(':')[1]);
});
Now the results array contains the three values customerid, dept, and dept

Here \S where S is capital is to get not space characters so it will get the word till first space match it, so it will match the word after : till the first space and we use /g to not only match the fisrt word and continue search in the string for other matches:
str.match(/:(\S*)/g).map(function(s){return s.substr(1)}).join(",")

regex replace all leading spaces with something

I'm trying to replace all of the leading spaces in a string with something
Here's what I tried so far
var str = ' testing 1 2 3 ',
regex = /^\s*/,
newStr = str.replace(regex, '.');
document.write(newStr)
I want to get a result like:
'.....testing 1 2 3 '
Is there something I'm missing?

Try this:
var s = " a b c";
print(s.replace(/^\s+/, function(m){ return m.replace(/\s/g, '.');}));
which prints:
...a b c

Alternative (ignores strnigs w/ no non-space)
var newStr = "";
newStr = (newStr = Array(str.search(/[^\s]/) + 1).join(".")) + str.substr(newStr.length);

What about:
/^([ ]+)/
I'm not sure \s does the trick, while a plain should be able to handle this!

This is even shorter.
var text = " a b c";
var result = s.replace(/\s/gy, ".");
console.log(result); // prints: "...a b c";
Why it works was explained for me here.

Replace last occurrence of character in string

Is there an easy way in javascript to replace the last occurrence of an '_' (underscore) in a given string?

You don't need jQuery, just a regular expression.
This will remove the last underscore:
var str = 'a_b_c';
console.log( str.replace(/_([^_]*)$/, '$1') ) //a_bc
This will replace it with the contents of the variable replacement:
var str = 'a_b_c',
replacement = '!';
console.log( str.replace(/_([^_]*)$/, replacement + '$1') ) //a_b!c

No need for jQuery nor regex assuming the character you want to replace exists in the string
Replace last char in a string
str = str.substring(0,str.length-2)+otherchar
Replace last underscore in a string
var pos = str.lastIndexOf('_');
str = str.substring(0,pos) + otherchar + str.substring(pos+1)
or use one of the regular expressions from the other answers
var str1 = "Replace the full stop with a questionmark."
var str2 = "Replace last _ with another char other than the underscore _ near the end"
// Replace last char in a string
console.log(
str1.substring(0,str1.length-2)+"?"
)
// alternative syntax
console.log(
str1.slice(0,-1)+"?"
)
// Replace last underscore in a string
var pos = str2.lastIndexOf('_'), otherchar = "|";
console.log(
str2.substring(0,pos) + otherchar + str2.substring(pos+1)
)
// alternative syntax
console.log(
str2.slice(0,pos) + otherchar + str2.slice(pos+1)
)

What about this?
function replaceLast(x, y, z){
var a = x.split("");
a[x.lastIndexOf(y)] = z;
return a.join("");
}
replaceLast("Hello world!", "l", "x"); // Hello worxd!

Another super clear way of doing this could be as follows:
let modifiedString = originalString
.split('').reverse().join('')
.replace('_', '')
.split('').reverse().join('')

Keep it simple
var someString = "a_b_c";
var newCharacter = "+";
var newString = someString.substring(0, someString.lastIndexOf('_')) + newCharacter + someString.substring(someString.lastIndexOf('_')+1);

var someString = "(/n{})+++(/n{})---(/n{})$$$";
var toRemove = "(/n{})"; // should find & remove last occurrence
function removeLast(s, r){
s = s.split(r)
return s.slice(0,-1).join(r) + s.pop()
}
console.log(
removeLast(someString, toRemove)
)
Breakdown:
s = s.split(toRemove) // ["", "+++", "---", "$$$"]
s.slice(0,-1) // ["", "+++", "---"]
s.slice(0,-1).join(toRemove) // "})()+++})()---"
s.pop() // "$$$"

Reverse the string, replace the char, reverse the string.
Here is a post for reversing a string in javascript: How do you reverse a string in place in JavaScript?

// Define variables
let haystack = 'I do not want to replace this, but this'
let needle = 'this'
let replacement = 'hey it works :)'
// Reverse it
haystack = Array.from(haystack).reverse().join('')
needle = Array.from(needle).reverse().join('')
replacement = Array.from(replacement).reverse().join('')
// Make the replacement
haystack = haystack.replace(needle, replacement)
// Reverse it back
let results = Array.from(haystack).reverse().join('')
console.log(results)
// 'I do not want to replace this, but hey it works :)'

This is very similar to mplungjan's answer, but can be a bit easier (especially if you need to do other string manipulation right after and want to keep it as an array)
Anyway, I just thought I'd put it out there in case someone prefers it.
var str = 'a_b_c';
str = str.split(''); //['a','_','b','_','c']
str.splice(str.lastIndexOf('_'),1,'-'); //['a','_','b','-','c']
str = str.join(''); //'a_b-c'
The '_' can be swapped out with the char you want to replace
And the '-' can be replaced with the char or string you want to replace it with

You can use this code
var str="test_String_ABC";
var strReplacedWith=" and ";
var currentIndex = str.lastIndexOf("_");
str = str.substring(0, currentIndex) + strReplacedWith + str.substring(currentIndex + 1, str.length);
alert(str);

This is a recursive way that removes multiple occurrences of "endchar":
function TrimEnd(str, endchar) {
while (str.endsWith(endchar) && str !== "" && endchar !== "") {
str = str.slice(0, -1);
}
return str;
}
var res = TrimEnd("Look at me. I'm a string without dots at the end...", ".");
console.log(res)