How to concat two javascript variables and regex expression - Stack Overflow

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I want to be able to concat two variables with a regular expression in the middle.

e.g.

var t1 = "Test1"
var t2 = "Test2"
var re = new RegEx(t1 + "/.*/" + t2);

So the result I want is an expression that matches this..

"Test1  this works   Test2"

How do I get a result where I am able to match any text that has Test1 and Test2 on the ends?

I want to be able to concat two variables with a regular expression in the middle.

e.g.

var t1 = "Test1"
var t2 = "Test2"
var re = new RegEx(t1 + "/.*/" + t2);

So the result I want is an expression that matches this..

"Test1  this works   Test2"

How do I get a result where I am able to match any text that has Test1 and Test2 on the ends?

• javascript
• regex
• concatenation

Share Improve this question Follow edited Oct 6, 2016 at 21:17 Barmar 784k5757 gold badges548548 silver badges659659 bronze badges asked Oct 6, 2016 at 21:16 rjg132234rjg132234 62033 gold badges1010 silver badges2121 bronze badges 2

• What are the / around .* for? – Barmar Commented Oct 6, 2016 at 21:18
• 2 Write the regex, then write JS Code to build that. don't just start slapping variables and operators around without a clear idea of what you're trying to acplish. – Marc B Commented Oct 6, 2016 at 21:18

Add a ment  | 

5 Answers 5

Sorted by: Reset to default 3

Try this (I use nodejs):

> var t1 = "Test1"
> var t2 = "Test2"
> var re = new RegExp('^' + t1 + '.*' + t2 + '$')
> re
/^Test1.*Test2$/
> re.test("Test1  this works   Test2")
true

Note

• .* as stated in ments, this means any character repeated from 0 to ~
• the slashes are automagically added when calling the RegExp constructor, but you can't have nested unprotected slashes delimiters
• to ensure Test1 is at the beginning, i put ^ anchor, and for Test2 at the end, I added $ anchor
• the regex constructor is not ReGex but RegExp (note the trailing p)

The RegExp constructor takes care of adding the forward slashes for you.

var t1 = "Test1";
var t2 = "Test2";
var re = new RegExp(t1 + ".*" + t2);

re.test("Test1 some_text Test2"); // true

You don't need regex:

var t1 = 'Test1';
var t2 = 'Test2';
var test = function(s) { return s.startsWith(t1) && s.endsWith(t2); };

console.log(test('Test1  this works   Test2'));
console.log(test('Test1 this does not'));

if you know the beginning and the end you can enforce that:

var re = new RegExp("^" + t1 + ".*" + t2 + "$");

Take care that the value of the two variables do not contain any special regex characters, or transform those values to escape any special regex characters.

Of course, also make sure that the regex in between matches what you want it to :-)

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