CODEWITHSUNDEEP
javascript
apelidoko
apelidoko

Reputation: 790

Javascript RegExp.prototype.test - how to regex values coming from an array

I want to check each values from my array if it matches the string, however it doesn't work when i'm using console.log(/^reg_arr[i]/.test(str1)); but when I use console.log(/^table/.test(str1)); it works

var str1 = 'table football';
var reg_arr = ["table","football"];
        
for(var i = 0, reg_arr_length = reg_arr.length; i < reg_arr_length; i++)
{
   console.log(/^reg_arr[i]/.test(str1)); /* doesnt work */
}

console.log(/^table/.test(str1)); /* this works */

Is there a problem with my syntax,

Thank you,

Upvotes: 0

Views: 636

Answers (2)

Matthias
Matthias

Reputation: 707

Using slashes to define a regular expression doesn't allow you to enter variables into the regular expression, that is, in the following example, str1 is checked to contain "test", not the value of the variable test.

var str1 = "hello";
var str2 = "Hello world";
console.log(/str1/i.test(str2))

To solve this issue, you need to create a new regular expression for each value in the array, something that can be done with new RegExp(str), instead of slashes.

var str1 = "hello";
var str2 = "hello world";
console.log(new RegExp(str1, "i").test(str2))

However, this method has a catch, characters from that string are not escaped. So new RegExp("test.hello") will match "test hello", because the dot is interpreted as a regular expression wildcard character and not a period. To fix that, we first have to manually escape any special characters in our search string (unless the things reg_arr are actually regular expressions). I took the code to do that from the middle of this MDN page.

var str1 = "hello"
var str2 = "hello world"

str1.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
console.log(new RegExp(str, "i").test(str2))

So without changing anything else, your final console.log could look like this:

console.log(new RegExp(reg_arr[i].replace(/[.*+?^${}()|[\]\\]/g, '\\$&')).test(str1));

Upvotes: 0

Kevin Qian
Kevin Qian

Reputation: 2720

Use new RegExp(source: string[, flags: string]) (simply RegExp(source: string[, flags: string]) is also working) 

var str1 = 'table football';
var reg_arr = ["table","football"];
        
for(var i = 0, reg_arr_length = reg_arr.length; i < reg_arr_length; i++)
{
   console.log(new RegExp(`^${reg_arr[i]}`).test(str1));
}

Upvotes: 1

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