Javascript Regular Expressions use variables

This article introduces some problems and solutions when using variables in Javascript Regular Expressions. It mainly describes the replacement and RegExp methods.

Example 1: replace with a variable

The replace function can be replaced by a regular expression that matches strings.

The problem we encountered today is that the regular expression has a variable. Take the actual situation today as an example:

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/(^ '+ Arr2 [I] +' |) | (| '+ arr2 [I] +' $ )/ Arr2 [I] is an array element and a variable. Str = str. replace (/(^ '+ arr2 [I] +' |) | (| '+ arr2 [I] +' $ )/,'');

This method cannot be replaced successfully. solution:

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Var reg = eval_r ('/(^' + arr2 [I] + '\ |) | (\ |' + arr2 [I] + '$ )/'); Str = str. replace (reg ,'');

If it is a direct variable, we can replace it as follows:

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Var match_str = 'bitch '; Var regex = "/," + match_str + ",/ig "; Var target_str = ", abcde, bitch, fghij ,"; Var val = target_str.replace (eval (regex ),","); Alert (val );

Val should be:, abcde, fghij,

Example 2: RegExp mode with variables

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Function checkBeginWithChar (str, minlen, maxlen, msg) { Minlen = minlen-1; Maxlen = maxlen-1; Var re = new RegExp ("^ [a-zA-Z] {1} ([a-zA-Z0-9]) {" + minlen + "," + maxlen + "} $ "); If (! Re.exe c (str )){ Alert (msg ); Return false ;} Return true; }

The above is a JavaScript function, which can be called as follows:

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If (! CheckBeginWithChar ("a123df", 6,12, "Your entered PIN must start with a letter and contain between 6 and 12 characters !")) Return false;

This is where variables are used. The following function does not use variables.

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Function checkBeginWithChar (str, msg) { Var patrn =/^ [a-zA-Z] {1} ([a-zA-Z0-9]) {5, 50} $ /; If (! Patrn.exe c (str )){ Alert (msg ); Return false; } Return true; }

Note: When no variable is available, the regular expression can have a backslash on both sides without being written as a string. If the variable is used, use new RegExp () and the strings in them do not have the two backslash.