JavaScript RegEx が入力の検証に失敗するのはなぜですか?

Struggles with RegEx Functionality in Javascript: A Case Study from "Regex Not Working"

In the context of the query referenced in the title, "Javascript RegEx Not Working," a user encountered an issue where a regular expression (regEx) consistently returned false, regardless of the input value. The code snippet provided in the inquiry is as follows:

<code class="javascript">function checkLegalYear() {
    var val = "02/2010"; 

    if (val != '') {
        var regEx = new RegExp("^(0[1-9]|1[0-2])/\d{4}$", "g");

        if (regEx.test(val)) {
            //do something
        }
        else {
            //do something
        }
    }
}</code>

The user attempted to validate year inputs using a RegEx and experienced unexpected results. Despite testing this code in multiple online editors, the RegEx continued to return false.

Addressing the Issue:

The root of the problem lies in the method used to create the RegEx object. When defining a RegEx from a string, backslash characters must be doubled up to prevent incorrect interpretation during the parsing process. To rectify this, the following code should be used:

<code class="javascript">var regEx = new RegExp("^(0[1-9]|1[0-2])//\\d{4}$", "g");</code>

Alternatively, it's recommended to use the RegEx syntax directly, which eliminates the need for doubling backslashes:

<code class="javascript">var regEx = /^(0[1-9]|1[0-2])//\\d{4}$/g;</code>

By implementing these modifications, the RegEx should now function as intended, validating year inputs and providing accurate results.

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