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replacing every second occurrence of a letter with a different letter or simbol

This pertains to any language that you think will work. Is there a way to change the look of a text input to replace every second space (space as in when the space bar is hit it makes a space) i need to a way almost like a counter that once it counts 2 spaces then it replaces that 2nd space to a letter or symbol. if someone could help me with this it would be amazing and the purpose is just to change the way the text looks in this way functionality does not matter as long as it reads like normal text. ( if it helps it would be every odd number of spaces gets changed.)
for example i want to be able to copy and paste something in like this> "i went down to the sea to pick up many sticks for my collection"
and have it return something like this
i%went down%to the%sea to%pick up%many sticks%for my%collection
the end goal is for the symbol to be a different color so it stands out from the text so if that would be possible that would be amazing.

I chose javascript, but there are multiple languages that you could choose and there are multiple ways to accomplish this. This is the train of thought that you should use when solving this problem:
Determine the characters that you want to replace
Determine the character that you want to replace it with
Since we don't want to replace every single one, what is the pattern/frequency that you want to replace found occurrences with.
For the 3rd question, you've said that you want to replace every other occurrence, so we need to keep track of the count of occurrences. And replace it when occurrence modulo 2 = 1. This says replace every odd occurrence.
I chose to use regex to find all the spaces in the sentence, have a counter n and increment the counter every time I find a space.
This leaves us with the following code:
const input = "i went down to the sea to pick up many sticks for my collection";
let n = 0;
const output = input.replace(/\s/g, (m, i, og) => {
return (n++ % 2) ? m : '%';
});
// output = "i%went down%to the%sea to%pick up%many sticks%for my%collection"
Also please take a look at String.prototype.replace() so you can learn about using regex, and to learn about what the function does. This will help you learn and solve similar problems by yourself in the future.

you can use a boolean variable to count odd and even spaces and string.prototyoe.replace with a callback function:
var str = 'i went down to the sea to pick up many sticks for my collection';
var odd = true;
str = str.replace(/\s/gi, (spaceChar)=>{
odd = !odd;
return !odd ? spaceChar : '%'; // this is what you wrote (every second)
// return odd ? spaceChar : '%'; // this is what your expected result shows (every second starting with the first occurence)
});

How to remove second whitespace in string, but not first using js

I have a small text field and if there is more than one whitespace I need to format the string and add a br tag in that second whitespace. If there isn;t then I do not need to do anything. I do not need to target the first or third (if there is one) and there will probably not be any after 3 as this is a short title field. the length of characters will be different and there is not consistent marker, like a comma of period or something, that I can target.
I was unable to find an answer that addressed this. I did find answers using regex but those all had markers like comma to target, I cannot find on that specifically will only target the second occurrence if there is one so any help would be great appreciated.
Code I have now, which targets only the first occurrence.
Array.prototype.forEach.call(awardscount, function() {
var string = $('#award-' + int).attr('data-award-title');
var refomrattedTitle = string.replace(" ", "<br>");
int++;
console.log(refomrattedTitle);
});

var test = "foo bar string test".replace(/([^\s]*\s[^\s]*)\s/, "$1<br/>");
console.log(test); // logs "foo bar<br/>string test"

split on words except when phrase contains that word

I am trying to split where clauses, I want to split text on AND|OR|NOT except when NOT is in the 'phrase' NOT IN or NOT LIKE or IS NOT NULL.
1st example:
DEVLDATE IS NOT NULL AND STATUS = D AND PICKUPDATE IS NULL
I expect 3 segments, splitting on the AND's, but not on the NOT in this instance.
2nd ex:
(NOT (STATUS IN ('A','X') )) AND LINEHAUL = 0
I want to split on this NOT & AND, also expecting 3 segments in this instance
I'm trying this look ahead from another almost similar example but it is not splitting at all. I have next to zero regex experience. Not sure what I'm missing or if it's even possible.
Thanks in advance.
var ignoreRegex = /(?!.*\b([NOT IN]|[NOT LIKE]|[NOT BETWEEN]|[IS NOT NULL])\b)(?=.*\b(AND|OR|NOT)\b)/g
var filterArray = filterBy.split(new RegExp(ignoreRegex));

Try with:
\b(AND|OR|NOT(?!\s+NULL|IN|LIKE))\b
DEMO
About your regex:
(?!.*\b([NOT IN]|[NOT LIKE]|[NOT BETWEEN]|[IS NOT NULL])\b)(?=.*\b(AND|OR|NOT)\b
[NOT IN] - this is character class [...] it will match character
which you put in in, so it can match: N,T,etc. not whole
word/sentence,
([NOT IN]|[NOT LIKE]|[NOT BETWEEN]|[IS NOT NULL]) - this whole part actually can match only one character, because it doesn't use any quantifires or intervals, it doesn't work as you expect at all,
so whole regex should match: some text with AND, OR or NOT, but if line within which the part was matched doesn't consist letters and spaces included in character classes..... so it will not match anything probably.

Javascript regex expression to replace multiple strings?

I've a string done like this: "http://something.org/dom/My_happy_dog_%28is%29cool!"
How can I remove all the initial domain, the multiple underscore and the percentage stuff?
For now I'm just doing some multiple replace, like
str = str.replace("http://something.org/dom/","");
str = str.replace("_%28"," ");
and go on, but it's really ugly.. any help?
Thanks!
EDIT:
the exact input would be "My happy dog is cool!" so I would like to get rid of the initial address and remove the underscores and percentage and put the spaces in the right place!
The problem is that trying to put a regex on Chrome "something goes wrong". Is it a problem of Chrome or my regex?

I'd suggest:
var str = "http://something.org/dom/My_happy_dog_%28is%29cool!";
str.substring(str.lastIndexOf('/')+1).replace(/(_)|(%\d{2,})/g,' ');
JS Fiddle demo.
The reason I took this approach is that RegEx is fairly expensive, and is often tricky to fine tune to the point where edge-cases become less troublesome; so I opted to use simple string manipulation to reduce the RegEx work.
Effectively the above creates a substring of the given str variable, from the index point of the lastIndexOf('/') (which does exactly what you'd expect) and adding 1 to that so the substring is from the point after the / not before it.
The regex: (_) matches the underscores, the | just serves as an or operator and the (%\d{2,}) serves to match digit characters that occur twice in succession and follow a % sign.
The parentheses surrounding each part of the regex around the |, serve to identify matching groups, which are used to identify what parts should be replaced by the ' ' (single-space) string in the second of the arguments passed to replace().
References:
lastIndexOf().
replace().
substring().

You can use unescape to decode the percentages:
str = unescape("http://something.org/dom/My_happy_dog_%28is%29cool!")
str = str.replace("http://something.org/dom/","");

Maybe you could use a regular expression to pull out what you need, rather than getting rid of what you don't want. What is it you are trying to keep?
You can also chain them together as in:
str.replace("http://something.org/dom/", "").replace("something else", "");

You haven't defined the problem very exactly. To get rid of all stretches of characters ending in %<digit><digit> you'd say
var re = /.*%\d\d/g;
var str = str.replace(re, "");

ok, if you want to replace all that stuff I think that you would need something like this:
/(http:\/\/.*\.[a-z]{3}\/.*\/)|(\%[a-z0-9][a-z0-9])|_/g
test
var string = "http://something.org/dom/My_happy_dog_%28is%29cool!";
string = string.replace(/(http:\/\/.*\.[a-z]{3}\/.*\/)|(\%[a-z0-9][a-z0-9])|_/g,"");

Javascript RegEx match problem

I have a sentence structure along the lines of
[word1]{word2} is going to the [word3]{word4}
I'm trying to use a javascript regex to match the words for replacement later. To do this, I'm working towards getting the following multi-dimensional array:
[["word1", "word2"],["word3","word4"]]
I'm currently using this regex for the job:
\[(.*?)\]\{(.*?)\}
However, it comes up with results like:
["[word1]{word2}", "word1", "word2"]
or worse. I don't really understand why because this regex seems to work in Ruby just fine, and I'm not really much of a regex expert in general to understand what's going on. I'm just curious if there are any javascript rege expert's out there to whom this answer is very clear and can guide me along with what's going on here. I appreciate any help!
Edit:
This is the code I'm using just to test the matching:
function convertText(stringText) {
var regex = /\[(.*?)\]\{(.*?)\}/;
console.log(stringText.match(regex));
}

I assume you are using the exec method of the regular expression.
What you are doing is almost correct. exec returns an array where the first element is the entire match and the remaining elements are the groups. You want only the elements at indexes 1 and 2. Try something like this, but of course store the results into an array instead of using an alert:
var string = '[word1]{word2} is going to the [word3]{word4}';
var pattern = /\[(.*?)\]\{(.*?)\}/g;
var m;
while(m = pattern.exec(string)) {
alert(m[1] + ',' + m[2]);
}
This displays two alerts:
word1,word2
word3,word4

What you're seeing is Japanese hiragana. Make sure your input is in English maybe?
Edited to say: Upon further review, it looks like a dictionary entry in Japanese. The 私 is kanji and the わたし is hiragana, a phonetic pronunciation of the kanji. FWIW, the word is "Watashi" which is one of the words for "I" (oneself) in Japanese.