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How to parse string value "(20)" to Integer in Javascript?

I'm working with a string "(20)". I need to convert it to an int. I read parseInt is a function which helps me to achieve that, but i don't know how.

Use string slicing and parseInt()
var str = "(20)"
str = str.slice(1, -1) // remove parenthesis
var integer = parseInt(str) // make it an integer
console.log(integer) // 20
One Line version
var integer = parseInt("(20)".slice(1, -1))
The slice method slices the string by the start and end index, start is 1, because that’s the (, end is -1, which means the last one - ), therefore the () will be stripped. Then parseInt() turns it into an integer.
Or use regex so it can work with other cases, credits to #adeithe
var integer = parseInt("(20)".match(/\d+/g))
It will match the digits and make it an integer
Read more:
slicing strings
regex

You can use regex to achieve this
var str = "(20)"
parseInt(str.match(/\d+/g).join())

Easy, use this
var number = parseInt((string).substr(2,3));

You need to extract that number first, you can use the match method and a regex \d wich means "digits". Then you can parse that number
let str = "(20)";
console.log(parseInt(str.match(/\d+/)));

Cleaner version of Hedy's
var str = "(20)";
var str_as_integer = parseInt(str.slice(1, -1))

I need help getting the first n characters of a string up to when a number character starts

I'm working with a string where I need to extract the first n characters up to where numbers begin. What would be the best way to do this as sometimes the string starts with a number: 7EUSA8889er898 I would need to extract 7EUSA But other string examples would be SWFX74849948, I would need to extract SWFX from that string.
Not sure how to do this with regex my limited knowledge is blocking me at this point:
^(\w{4}) that just gets me the first four characters but I don't really have a stopping point as sometimes the string could be somelongstring292894830982 which would require me to get somelongstring

Using \w will match a word character which includes characters and digits and an underscore.
You could match an optional digit [0-9]? from the start of the string ^and then match 1+ times A-Za-z
^[0-9]?[A-Za-z]+
Regex demo
const regex = /^[0-9]?[A-Za-z]+/;
[
"7EUSA8889er898",
"somelongstring292894830982",
"SWFX74849948"
].forEach(s => console.log(s.match(regex)[0]));

Can use this regex code:
(^\d+?[a-zA-Z]+)|(^\d+|[a-zA-Z]+)
I try with exmaple and good worked:
1- somelongstring292894830982 -> somelongstring
2- 7sdfsdf5456 -> 7sdfsdf
3- 875werwer54556 -> 875werwer

If you want to create function where the RegExp is parametrized by n parameter, this would be
function getStr(str,n) {
var pattern = "\\d?\\w{0,"+n+"}";
var reg = new RegExp(pattern);
var result = reg.exec(str);
if(result[0]) return result[0].substr(0,n);
}

There are answers to this but here is another way to do it.
var string1 = '7EUSA8889er898';
var string2 = 'SWFX74849948';
var Extract = function (args) {
var C = args.split(''); // Split string in array
var NI = []; // Store indexes of all numbers
// Loop through list -> if char is a number add its index
C.map(function (I) { return /^\d+$/.test(I) === true ? NI.push(C.indexOf(I)) : ''; });
// Get the items between the first and second occurence of a number
return C.slice(NI[0] === 0 ? NI[0] + 1 : 0, NI[1]).join('');
};
console.log(Extract(string1));
console.log(Extract(string2));
Output
EUSA
SWFX7

Since it's hard to tell what you are trying to match, I'd go with a general regex
^\d?\D+(?=\d)

What does this obfuscated javascript snippet mean/do?

I cannot understand what this little snippet: var num = str.replace(/[^0-9]/g, ''); does.
Context:
function retnum(str) {
var num = str.replace(/[^0-9]/g, '');
var liczba = parseInt(num);
return liczba;
}

This JavaScript snippet will rip out anything that is not (the ^ part of the regular expression means "not") a number in str and then return an integer cast from the result as liczba. See my comments:
// This function will return a number from a string that may contain other characters.
// Example: "1.23" -> 123
// Example: "a123" -> 123
// Example: "hg47g*y#" -> 47
function retnum(str) {
// First let's replace everything in str that is not a number with "" (nothing)
var num = str.replace(/[^0-9]/g, '');
// Let's use JavaScript's built in parseInt() to parse an Integer from the remaining string (called "num")
var liczba = parseInt(num);
// Let's now return that Integer:
return liczba;
}
By the way, "liczba" means number in Polish :-)

This function takes a string, strips all non-number characters from it, turns the string into an integer, and returns the integer. The line you're asking about specifically is the part that strips out all non-number characters from the initial string, using the string.replace method.

It's not obfuscated, it's using a regular expression.
The expression matches all things which are not numbers then removes them. 0-9 means "any digit" and the ^ means "not". The g flag means to check the entire string instead of just the first match. Finally, the result is converted to a number.
Example:
var input = 'abc123def456';
var str = input.replace(/[^0-9]/g, '');
var num = parseInt(str);
document.querySelector('pre').innerText = num;
<pre></pre>

It literally just replaces anything which is not a number with a blank ('').

Javascript extract numbers from a string

I want to extract numbers from a string in javascript like following :
if the string = 'make1to6' i would like to extract the numeric character before and after the 'to' substring in the entire string. i.e. 1 and 6 are to be extracted
The length of the string is not fixed and can be a max of 10 characters in length.The number can be of max two digits on either side of 'to' in the string.
Possible string values :
sure1to3
ic3to9ltd
anna1to6
joy1to4val
make6to12
ext12to36
thinking of something like :
function beforeTo(string) {
return numeric_value_before_'to'_in_the_string;
}
function afterTo(string) {
eturn numeric_value_after_'to'_in_the_string;
}
i will be using these returned values for some calculations.

Here's an example function that will return an array representing the two numbers, or null if there wasn't a match:
function extractNumbers(str) {
var m = /(\d+)to(\d+)/.exec(str);
return m ? [+m[1], +m[2]] : null;
}
You can adapt that regular expression to suit your needs, say by making it case-insensitive: /(\d+)to(\d+)/i.exec(str).

You can use a regular expression to find it:
var str = "sure1to3";
var matches = str.match(/(\d+)to(\d+)/);
if (matches) {
// matches[1] = digits of first number
// matches[2] = digits of second number
}

What's a good RegExp that will strip out all characters except Integers from a string?

I'm new to using regexp, can someone give me the regexp that will strip out everything but an integer from a string in javascript?
I would like to take the string "http://www.foo.com/something/1234/somethingelse" and get it down to 1234 as an integer.
Thanks

var str = "something 123 foo 432";
// Replace all non-digits:
str = str.replace(/\D/g, '');
alert(str); // alerts "123432"
In response to your edited question, extracting a string of digits from a string can be simple, depending on whether you want to target a specific area of the string or if you simply want to extract the first-occurring string of digits. Try this:
var url = "http://www.foo.com/something/1234/somethingelse";
var digitMatch = url.match(/\d+/); // matches one or more digits
alert(digitMatch[0]); // alerts "1234"
// or:
var url = "http://x/y/1234/z/456/v/890";
var digitMatch = url.match(/\d+/g); // matches one or more digits [global search]
digitMatch; // => ['1234', '456', '890']

This is just for integers:
[0-9]+
The + means match 1 or more, and the [0-9] means match any character from the range 0 to 9.

uri = "http://www.foo.com/something/1234/somethingelse";
alert(uri.replace(/.+?\/(\d+)\/.+/, "$1"))

Just define a character-class that requires the values to be numbers.
/[^0-9]/g // matches anything that is NOT 0-9 (only numbers will remain)