passing variable to a regexp in javascript
Possible Duplicate:
Escape string for use in Javascript regex
I have a msg like this:
Max {0} chars allowed in {1}
And I have a function to create a message using the arguments passed as
for(var i = 0; i < agrs.length; i++){
reg = new RegExp('{'+i+'}', 'gi');
key = key.replace(reg,agrs[i])
}
The problem is that it's not able to take the param i to create the reg exp.
What's the way to achieve this?
Your regexp is /{0}/gi since you create it from a string. And it is not a valid expression. You need to escape { in the regexp because it has a special meaning in the regexp syntax, so it should be:
new RegExp('{'+i+'}', 'gi');
which is /{0}/gi . You need to escape the escaping in the string.
I would strongly encourage you to use the functional form of String.replace() to solve your problem, rather than trying to parametrize the regexp in a for-loop that iterates over {0},{1},etc.
In other words, rather than look for '{0}' or '{1}', just look for '{([0-9]+)}' (ie {}'s surrounding an arbitrary number, and pass a function to the replace() function to intelligently replace these expressions based on the number between the {}'s. This lets you use a RegExp literal which you can write as /{([0-9]+)}/ rather than mess around with escape characters in strings.
Something like this:
s='the song says {0} little {1} little {2} little-endians';
args=['zero','one','two'];
new_string = s.replace(/{([0-9]+)}/g, function(wholematch,firstmatch)
{return args[(+firstmatch)]; }
);
which yields
the song says zero little one little two little-endians
See this similar question.
edit: if you want to leave alone items that are greater than the length of your args list, make sure to sanity-check the parameter number:
s='the song says {0} little {1} little {2} little-endians,n'+
' {3} little {4} little {5} little-endians';
args=['zero','one','two'];
new_string = s.replace(/{([0-9]+)}/g, function(wholematch,firstmatch)
{var i = +firstmatch; return i < args.length ? args[i] : wholematch;}
);
which yields
the song says zero little one little two little-endians,
{3} little {4} little {5} little-endians
I think your second line is supposed to be
reg = new RegExp('{'+i+'}', 'gi');
but I don't know if that's your only problem or not.
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