When using the test() method in JavaScript with regular expressions, it may return true even if not all characters match, even when using

When attempting input validation in a textarea, I encountered the following issue:

const re= /^[0-9A-Za-zÀ-ÿ\s\’\'\:\.\-\,\!\[\]\(\)\@\&\?]+?$/im;
re.test(control.value)

During the first test:

+

The result was false as expected.

However, during the second test:

+
1234

The test() returned true, even though it should have still been false due to the presence of an invalid character and the use of ^...$.

If you can shed light on this issue, it would be greatly appreciated.

Thanks!

Answer №1

The main issue lies with the m flag - it is used to match the start and end of a line, not the entire string. As a result, even if only one line adheres to the regex pattern, the whole string will be considered valid.

To rectify this, you should include newline characters in your character set (if they are permitted) and remove the m flag. This adjustment ensures that the ^ and $ symbols will strictly match the beginning and end of the string:

const re= /^[0-9A-Za-zÀ-ÿ\s\’\'\:\.\-\,\!\[\]\(\)\@\&\?\n]+?$/i;
const validate = str => re.test(str);
document.querySelector('textarea').onchange = function() {
  console.log(re.test(this.value));
}
<textarea>
</textarea>

Answer №2

Feel free to take a look at the example here. In this case, the 'm' flag has been added to signify that '^ and $ matches start and end of line'

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