JavaScript RegEx $1 Tokens

[masterjake]

Hi. I'm having a problem. I have various text fields with ID's of a letter and a number e.g. "A1", "C3", etc.

When this JavaScript function runs it is suppose to replace all occurrences of "{stuff here}" with the value at the cell number within the {}.

For example, if they type in "{A1}+{B2}" then the JavaScript should find {A1} and replace it with the value of the element who's ID is "A1."

Here is what I have. I know it's a problem with the "$1."

var editedExpression = eqvalue.replace(/\{(.+?)\}/g, document.getElementById("$1").value);

 

[VPmase]

Where does the $1 come in other than that line?

 

[ah-blabla]

//UPDATE: Ignore this post, misson actually knows what he's on about, so read his post.

Where does the $1 come in other than that line?

I was wondering the same. If $1 is a variable, then remove the quotation marks around it, since here you are passing $1 as the name of an element. However, javascript variables aren't usually written with $ signs... Unless you are using a variable from php, in which case you would have to enclose it in <?php ?> tags if it is external, or add a . on either side of the $1 to concatenate it as part of a string you are doing something with.

 

[misson]

document.getElementById(...) is being called before eqvalue.replace(...) (remember, in f(..., g(...), ...), the call to g(...) must be evaluated before f is called). The solution is to use an anonymous function:

var editedExpression = eqvalue.replace(/\{(.+?)\}/g, 
        function(matched, id) { return document.getElementById(id).value; });

The matched substrings are passed as parameters to the function; $& is passed in arguments[0] and $n in arguments[n].

Also note that the $n signifier for positional parameters is only supported in a few contexts: a regular expression and a plain string replacement. There are also properties of RegExp named $n that hold the matches from the last successful match; while they have the same signifiers, they're different beasts. "$n" has no special meaning within a function replacement.

 

[masterjake]

Thanks man, that code worked.

In every other language I've used for RegEx replacement (generally by means of preg_replace), all of the returned (groups) were placed into $variables.

I figured JavaScript would be the same.

 

[misson]

In every other language I've used for RegEx replacement (generally by means of preg_replace), all of the returned (groups) were placed into $variables.

True of Perl, but not PHP. "$1" isn't a valid PHP variable name; PHP variable names must start with an underscore or a letter. Backreferences of the form "$n" are only supported in regular expressions and replacement strings.