Detect If Variable Is A Pattern

Question

I cannot figure out a way to detect if a variable is a regex. But I also need to figure out if it is an object so I cannot use the typeof(regex) === 'object' and rely on it since it may since the if statement will execute it as if it was a regex. But I would like it to work in legacy browsers too. Any help will be most appreciated.

var regex= /^[a-z]+$/;

//...Some code that could alter the regex variable to become an object variable.



if (typeof(regex) === 'object') {
    console.log(true);
}

score 0 · Accepted Answer · answered Sep 06 '17 at 01:24

0

You can use instanceOf

var regex= /^[a-z]+$/;

//...Some code that could alter the regex variable to become an object variable.



if (regex instanceof RegExp) {
    console.log(true);
}

answered Sep 06 '17 at 01:24

bluetoft

5,373
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DjaouadNM · Answer 2 · 2017-09-06T18:32:22.810

0

There are ways to do this, they include :

var regex= /^[a-z]+$/;

// constructor name, a string
// Doesn't work in IE
console.log(regex.constructor.name === "RegExp"); // true
// instanceof, a boolean
console.log(regex instanceof RegExp); // true
// constructor, a constructor
console.log(regex.constructor == RegExp); // true

edited Sep 06 '17 at 18:32

answered Sep 06 '17 at 01:26

DjaouadNM

22,013
4
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The first one doesn't work in IE. Don't test for function names. – Bergi Sep 06 '17 at 01:37
@Bergi That's why I mentioned the other methods. – DjaouadNM Sep 06 '17 at 11:24
But why mention it all? It just increases the chances that someone reading the answer picks up a bad practice (especially as it's mentioned first). – Bergi Sep 06 '17 at 18:22
1

@Bergi I get it, I just added a comment about it. – DjaouadNM Sep 06 '17 at 18:32

Detect If Variable Is A Pattern

2 Answers2