Develop Reference

Using JS to modify user input for REGEXP search

I'm taking user input from a searchbar and modifying it to a regexp. From there I can search a json file for valid values and return them. It works fine with input without quotes, but with them, I'm appending "\Q" and "\E" so I can find the entirety of the string (with spaces and other special characters).
if (searchField.includes('"')){
var tempexpress = searchField.substring(1,searchField.length-1);
var tempexpress = "\\Q" + tempexpress + "\\E";
var expression = new RegExp(tempexpress);
} else {
var tempexpress = searchField.replace('(',"\\(");
var tempexpress = tempexpress.replace(')',"\\)");
var tempexpress = tempexpress.replace(/'/g,"\\'");
var tempexpress = tempexpress.replace('*',"\.");
var expression = new RegExp(tempexpress, "i");
};
if (value.data.label.search(expression) != -1){
console.log('found it');
}
If I input "QTT6" into the search field (with quotes for a literal), then it creates the following regexp: /\QQTT6\E/
In my testing, I found that it doesn't match to QTT6 for some reason and I'm not sure why. Any help is appreciated.
Also I'm very new to JS and Jquery, so sorry if my code isn't very well put together.

Per Kelly's comment:
In JS you need to use ^ and $ instead of \Q and \E.
For more information, see the MDN docs on Regex Assertions:
^:
Matches the beginning of input. If the multiline flag is set to true, also matches immediately after a line break character. For example, /^A/ does not match the "A" in "an A", but does match the first "A" in "An A".
Note: This character has a different meaning when it appears at the start of a character class.
$:
Matches the end of input. If the multiline flag is set to true, also matches immediately before a line break character. For example, /t$/ does not match the "t" in "eater", but does match it in "eat".

JS conditional RegEx that removes different parts of a string between two delimiters

I have a string of text with HTML line breaks. Some of the <br> immediately follow a number between two delimiters «...» and some do not.
Here's the string:
var str = ("«1»<br>«2»some text<br>«3»<br>«4»more text<br>«5»<br>«6»even more text<br>");
I’m looking for a conditional regex that’ll remove the number and delimiters (ex. «1») as well as the line break itself without removing all of the line breaks in the string.
So for instance, at the beginning of my example string, when the script encounters »<br> it’ll remove everything between and including the first « to the left, to »<br> (ex. «1»<br>). However it would not remove «2»some text<br>.
I’ve had some help removing the entire number/delimiters (ex. «1») using the following:
var regex = new RegExp(UsedKeys.join('|'), 'g');
var nextStr = str.replace(/«[^»]*»/g, " ");
I sure hope that makes sense.
Just to be super clear, when the string is rendered in a browser, I’d like to go from this…
«1»
«2»some text
«3»
«4»more text
«5»
«6»even more text
To this…
«2»some text
«4»more text
«6»even more text
Many thanks!

Maybe I'm missing a subtlety here, if so I apologize. But it seems that you can just replace with the regex: /«\d+»<br>/g. This will replace all occurrences of a number between « & » followed by <br>
var str = "«1»<br>«2»some text<br>«3»<br>«4»more text<br>«5»<br>«6»even more text<br>"
var newStr = str.replace(/«\d+»<br>/g, '')
console.log(newStr)
To match letters and digits you can use \w instead of \d
var str = "«a»<br>«b»some text<br>«hel»<br>«4»more text<br>«5»<br>«6»even more text<br>"
var newStr = str.replace(/«\w+?»<br>/g, '')
console.log(newStr)

This snippet assumes that the input within the brackets will always be a number but I think it solves the problem you're trying to solve.
const str = "«1»<br>«2»some text<br>«3»<br>«4»more text<br>«5»<br>«6»even more text<br>";
console.log(str.replace(/(«(\d+)»<br>)/g, ""));
/(«(\d+)»<br>)/g
«(\d+)» Will match any brackets containing 1 or more digits in a row
If you would prefer to match alphanumeric you could use «(\w+)» or for any characters including symbols you could use «([^»]+)»
<br> Will match a line break
//g Matches globally so that it can find every instance of the substring
Basically we are only removing the bracketed numbers if they are immediately followed by a line break.

Javascript/Node.JS find text between two strings, multiple times

I need to find the text between begin and end, multiple times. I have a regex expression setup, but it only finds the first instance. Is there a way that I could make it find every "text" and then I can call them separately as an array, i.e., instances[1], instances[2], etc. I am using Node.JS so I cannot use the DOM as some other answers have applied.
begin
text
end
begin
text
end
begin
text
end
begin
text
end

Yes append /g to the end of the regular expression to match all occurrences like so:
let myArr = "begin middle end".match(/regularExpression/g)
Below is a snippet for your purposes:
var input = "begin middle end";
var regex = /begin\s(.*)\send/g;
var matches;
while (matches = regex.exec(input)) {
console.log(matches);
console.log('Middle text is: ' + matches[1]);
}

The expression will be something like this:
/begin\n([\w ]+)\nend/g
Note the g at the end for global match.

Test if a sentence is matching a text declaration using regex

I want to test if a sentence like type var1,var2,var3 is matching a text declaration or not.
So, I used the following code :
var text = "int a1,a2,a3",
reg = /int ((([a-z_A-Z]+[0-9]*),)+)$/g;
if (reg.test(text)) console.log(true);
else console.log(false)
The problem is that this regular expression returns false on text that is supposed to be true.
Could someone help me find a good regular expression matching expressions as in the example above?

You have a couple of mistekes.
As you wrote, the last coma is required at the end of the line.
I suppose you also want to match int abc123 as correct string, so you need to include letter to other characters
Avoid using capturing groups for just testing strings.
const str = 'int a1,a2,a3';
const regex = /int (?:[a-zA-Z_](?:[a-zA-Z0-9_])*(?:\,|$))+/g
console.log(regex.test(str));

You will need to add ? after the comma ,.
This token ? matches between zero and one.
Notice that the last number in your text a3 does not have , afterward.
int ((([a-z_A-Z]+[0-9]*),?)+)$

How to detect a series of characters in a string?

For example, I have a string:
"This is the ### example"
I would like to substring the ### out of the above string?
The number of Hash keys may vary, so I would like to find out and replace the ### pattern with, say, 001 for example.
Can anybody help?

You can also do a replace. I am familiar with the C# version of this,
string stringValue = "Thia is the ### example";
stringValue.Replace("###", "");
This would remove ### completely from the above string. Again you would have to know the exact string.
In JavaScript, it's similar - .replace (with a lowercase r) is used. So:
var stringValue = "This is the ### example";
var replacedValue = stringValue.replace('###', '');

You'll want to investigate either "Regular Expressions" for this, or, if you know the precise position and length of the characters you are interested in, you can simply use String's .substring method.

If you want to capture multiple # characters, then you'll need regular expressions:
var myString = "This is #### the example";
var result = myString.replace(/#+/g, '');
If you want to remove the space too, you can use the regex /#+\s|\s#+|#+/.

If the rest of the string is known, just get the part that you need:
var example = str.substr(12, str.length - 20);

The javascript match method will return an array of substrings matching a regular expression. You can use this to determine the number of matching characters to be replaced. Assuming you want to replace each octothorpe with a random digit, you could use code like this:
var exampleStr = "This is the ### example";
var swapThese = exampleStr.match(/#/g);
if (swapThese) {
for (var i=0;i<swapThese.length;i++) {
var swapThis = new RegExp(swapThese[i]);
exampleStr = exampleStr.replace(swapThis,Math.floor(Math.random()*9));
}
}
alert(exampleStr); // or whatever you want to do with it
Note that the code only loops the length of the array if it's present: if (swapThese) {
This check is necessary because if the match method finds no matches, it returns null rather than an empty array. Trying to iterate through null value will break.