Question

Disclaimer: I realize asking “Why doesn’t my regular expression work” is pretty amateur.

I have looked at the documentation, though I’m just plain struggling. I have a url (as a string) and what I want is to replace the placeholders (i.e. {objectID} and {queryTerm}

For a while now, I’ve been making attempts like this:

var _serviceURL = "http://my-server.com/rest-services/someObject/{objectID}/entries?term={queryTerm}";

var re1 = new RegExp("/{([A-Za-z])+}","gi");  
var re2 = new RegExp("/{([A-Za-z]+)}+","gi");  
var re3 = new RegExp("/{([A-Za-z])+}","gi");  
var re4 = new RegExp("/({[A-Za-z]+})+","gi");  
var re5 = new RegExp("({[A-Za-z]+})+","gi");  
var re6 = new RegExp("({[A-Za-z]}+)*","g");  
var re6a = new RegExp("({([a-z]+)})+","gi");  

var re7 = /{([^}]+)}/g;

var tokens =  re6A.exec(_serviceURL);
if (null != tokens.length ){
    for(i = 0; i < tokens.length; i++){
        var t = tokens[i];
        console.log("tokens[i]: " + t);
    }            
}
else {
    console.log("RegEx fail...")
}

re6a above produces an array like this upon execution:

tokens: Array[3]
    0: "{objectID}"
    1: "{objectID}"
    2: "objectID"

Related to the scenario above:

1. Why is it I’m never getting the queryTerm ?
2. Does the RegExp ‘i’ (ignore case) flag mean I can list a character class like [a-z] and also capture [A-Z] ?
3. Which method of constructing a RegExp object is better? ...new RegExp(...); or var regExp = /{([^}]+)}/g; . In terms of “what’s better”, what I mean is cross-browser compatibility and as similar to other RegEx implementations (if I’m learning RegEx, I want to get the most value I can out of it).

Answer 1

Does the RegExp i (ignore case) flag mean I can list a character class like [a-z] and also capture [A-Z]?

Yes, it’ll capture them all.

Which method of constructing a RegExp object is better? new RegExp(...) or var regExp = /{([^}]+)}/g;? In terms of “what’s better”, what I mean is cross-browser compatibility and as similar to other RegEx implementations (if I’m learning RegEx, I want to get the most value I can out of it).

You should definitely use the literal notation.
It gets compiled once at runtime, instead of every time you use it.
They’re both equally cross browser compatible.

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All that said, I’d use this:

_serviceURL.match(/[^{}]+(?=})/g);

Here’s the fiddle: http://jsfiddle.net/CAugU/

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Here’s an explanation of the above regex:

[    opens the character set
 ^    negates the set. Will only match whatever is NOT in these brackets
 {}   match anything that is NOT a curly brace
]    close the character set
+    match that as many times as possible
(?=  ascertain that it is possible to match the following here (won't be included in the match, this is called a lookahead)
 }    match a curly brace
)    close the lookahead