How do you use a variable in a regular expression?
I would like to create a String.replaceAll() method in JavaScript and I'm thinking that using a RegEx would be most terse way to do it. However, I can't figure out how to pass a variable in to a RegEx. I can do this already which will replace all the instances of "B" with "A".
"ABABAB".replace(/B/g, "A");
But I want to do something like this:
String.prototype.replaceAll = function(replaceThis, withThis) {
this.replace(/replaceThis/g, withThis);
};
But obviously this will only replace the text "replaceThis"...so how do I pass this variable in to my RegEx string?
Instead of using the /regex/g syntax, you can construct a new RegExp object:
var replace = "regex";
var re = new RegExp(replace,"g");
You can dynamically create regex objects this way. Then you will do:
"mystring".replace(re, "newstring");
As Eric Wendelin mentioned, you can do something like this:
str1 = "pattern"
var re = new RegExp(str1, "g");
"pattern matching .".replace(re, "regex");
This yields "regex matching ." . However, it will fail if str1 is "." . You'd expect the result to be "pattern matching regex" , replacing the period with "regex" , but it'll turn out to be...
regexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregex
This is because, although "." is a String, in the RegExp constructor it's still interpreted as a regular expression, meaning any non-line-break character, meaning every character in the string. For this purpose, the following function may be useful:
RegExp.quote = function(str) {
return str.replace(/([.?*+^$[](){}|-])/g, "$1");
};
Then you can do:
str1 = "."
var re = new RegExp(RegExp.quote(str1), "g");
"pattern matching .".replace(re, "regex");
yielding "pattern matching regex" .
"ABABAB".replace(/B/g, "A");
As always: don't use regex unless you have to. For a simple string replace, the idiom is:
'ABABAB'.split('B').join('A')
Then you don't have to worry about the quoting issues mentioned in Gracenotes's answer.
链接地址: http://www.djcxy.com/p/2152.html下一篇: 你如何在正则表达式中使用变量？