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jQuery / Javascript replace multiple occurences not working

I'm trying to replace multiple occurrences of a string and nothing seems to be working for me. In my browser or even when testing online. Where am I going wrong?
str = '[{name}] is happy today as data-name="[{name}]" won the match today. [{name}] made 100 runs.';
str = str.replace('/[{name}]/gi','John');
console.log(str);
http://jsfiddle.net/SXTd4/
I got that example from here, and that too wont work.

You must not quote regexes, the correct notation would be:
str = str.replace(/\[{name}\]/gi,'John');
Also, you have to escape the [], because otherwise the content inside is treated as character class.
Updating your fiddle accordingly makes it work.
There are two ways declaring regexes:
// literal notation - the preferred option
var re = /regex here/;
// via constructor
var re = new Regexp('regex here');

You should not put your regex in quotes and you need to escape []
Simply use
str = str.replace(/\[{name}\]/gi,'John');
DEMO

While there are plenty of regex answers here is another way:
str = str.split('[{name}]').join('John');

The characters [ ] { } should be escaped in your regular expression.

Regexp for floating number

I found this regexp for validating floats. But I cant see how 2-1 will accepted. The below evaluates to true. I can't use parseFloat because I need to be able to accept "," instead of "." also. I wrote re2, same result though.
var re1 = new RegExp("^[-+]?[0-9]*\.?[0-9]+$");
console.log(re1.test("2-1"));
var re2 = new RegExp("^([0-9]+)\.([0-9]+)$");
console.log(re2.test("2-1"));

If you generate the regex using the constructor function, you have to to escape the backslash, i.e. \ becomes \\:
var re1 = new RegExp("^[-+]?[0-9]*\\.?[0-9]+$");
Another option is to use the literal syntax which doesn't require escaping:
var re1 = /^[-+]?[0-9]*\.?[0-9]+$/

Sometimes when you create a regex string, you even have to escape the backslash; this can of course be done with a backslash, so the final regex looks something like "\\.*", etc.
Doing this, I was able to get the correct results, as seen here:
var re1 = new RegExp("^[-+]?[0-9]*\\.?[0-9]+$");
console.log(re1.test("2-1"));
var re2 = new RegExp("^([0-9]+)\\.([0-9]+)$");
console.log(re2.test("2-1"));
console.log(re1.test("2.1"));
console.log(re2.test("2.1"));​

What about replacing a comma (",") with a period (".") and then using parseFloat?

Javascript regex grouping

I am trying to create a regular expression that would easily replace an input name such as "holes[0][shots][0][unit]" to "holes[0][shots]1[unit]". I'm basically cloning a HTML input and would like to make sure its position is incremented.
I got my regex built and working correctly using this (awesome) tool : http://gskinner.com/RegExr/
Here is my current regex :
(.*\[shots\]\[)([0-9]+)(\].*\])
and I am using a replace such as :
$12$3
this transforms "holes[0][shots][0][unit]" into "holes[0][shots][2][unit]". This is exactly want I want. However, when I try this in javascript (http://jsfiddle.net/PH2Rh/) :
var str = "holes[0][shots][0][units]";
var reg =new RegExp("(.*\[shots\]\[)([0-9]+)(\].*\])", "g");
console.log(str.replace(​reg,'$1'));​​​​​​​​​​​​​​​​​​​​​​​​
I get the following output : holes[0
I don't understand how my first group is supposed to represent "holes[0", since I included the whole [shots][ part in it.
I appreciate any inputs on this. THank you.

In strings, a single \ is not interpreted as a Regex-escaping character. To escape the bracket within string literals, you have to use two backslashes, \\:
var reg = new RegExp("(.*\\[shots\\]\\[)([0-9]+)(\\].*\\])", "g");
A preferable solution is to use RegEx literals:
var reg = /(.*\[shots\]\[)([0-9]+)(\].*\])/g;

Looks like, this works:
var str = "holes[0][shots][0][units]";
var reg = /(.*\[shots\]\[)([0-9]+)(\].*\])/;
console.log(str.replace(​reg,'$1'));​​​​​​​​​​​​​​​​​​​​​​​​

RegExp.test not working?

I am trying to validate year using Regex.test in javascript, but no able to figure out why its returning false.
var regEx = new RegExp("^(19|20)[\d]{2,2}$");
regEx.test(inputValue) returns false for input value 1981, 2007
Thanks

As you're creating a RegExp object using a string expression, you need to double the backslashes so they escape properly. Also [\d]{2,2} can be simplified to \d\d:
var regEx = new RegExp("^(19|20)\\d\\d$");
Or better yet use a regex literal to avoid doubling backslashes:
var regEx = /^(19|20)\d\d$/;

Found the REAL issue:
Change your declaration to remove quotes:
var regEx = new RegExp(/^(19|20)[\d]{2,2}$/);

Do you mean
var inputValue = "1981, 2007";
If so, this will fail because the pattern is not matched due to the start string (^) and end string ($) characters.
If you want to capture both years, remove these characters from your pattern and do a global match (with /g)
var regEx = new RegExp(/(?:19|20)\d{2}/g);
var inputValue = "1981, 2007";
var matches = inputValue.match(regEx);
matches will be an array containing all matches.

I've noticed, for reasons I can't explain, sometimes you have to have two \\ in front of the d.
so try [\\d] and see if that helps.

Passing regex modifier options to RegExp object

I am trying to create something similar to this:
var regexp_loc = /e/i;
except I want the regexp to be dependent on a string, so I tried to use new RegExp but I couldn't get what i wanted.
Basically I want the e in the above regexp to be a string variable but I fail with the syntax.
I tried something like this:
var keyword = "something";
var test_regexp = new RegExp("/" + keyword + "/i");
Basically I want to search for a sub string in a larger string then replace the string with some other string, case insensitive.
regards,
alexander

You need to pass the second parameter:
var r = new RegExp(keyword, "i");
You will also need to escape any special characters in the string to prevent regex injection attacks.

You should also remember to watch out for escape characters within a string...
For example if you wished to detect for a single number \d{1} and you did this...
var pattern = "\d{1}";
var re = new RegExp(pattern);
re.exec("1"); // fail! :(
that would fail as the initial \ is an escape character, you would need to "escape the escape", like so...
var pattern = "\\d{1}" // <-- spot the extra '\'
var re = new RegExp(pattern);
re.exec("1"); // success! :D

When using the RegExp constructor, you don't need the slashes like you do when using a regexp literal. So:
new RegExp(keyword, "i");
Note that you pass in the flags in the second parameter. See here for more info.

Want to share an example here:
I want to replace a string like: hi[var1][var2] to hi[newVar][var2].
and var1 are dynamic generated in the page.
so I had to use:
var regex = new RegExp("\\\\["+var1+"\\\\]",'ig');
mystring.replace(regex,'[newVar]');
This works pretty good to me. in case anyone need this like me.
The reason I have to go with [] is var1 might be a very easy pattern itself, adding the [] would be much accurate.

var keyword = "something";
var test_regexp = new RegExp(something,"i");

You need to convert RegExp, you actually can create a simple function to do it for you:
function toReg(str) {
if(!str || typeof str !== "string") {
return;
}
return new RegExp(str, "i");
}
and call it like:
toReg("something")