难以将正则表达式匹配到过滤方法

Question

Doing a challenge, went a much more complicated route than the solution provided, but now I want to solve the regex filter issue I've stumbled upon.

Everything works fine until the the second to last line of the currentFileExt() function. I originally planned on using map, but after looking through similar StackOverflow solutions I figured .filter() is more appropriate. Sadly, I can't seem to get the filter to check against the regex I provided.

Perhaps it's a misunderstanding on my part, but I am using the filter to match each string element of the split toArr array, if it matches the regex it should get filtered. Unfortunately, that doesnt appear to be happening.

function findFileName(fileName) {
    let detect = (fileName.match(/\.+/g)) ? currentFileExt() : alert("Please enter");
    return detect;

    function currentFileExt() {
        let toArr = fileName.split('');
        let fileExtArr = [];
        // let validCharacter = new RegExp(/\.[a-z]+/, 'g');
        let validCharacter = /\.[a-z]+/;
        fileExtArr = toArr.filter( (element) => { element.match(validCharacter) });
        return fileExtArr.join('');
    }  
}

findFileName('java.java');

Answer 1

One of the issues is that your filter callback function isn't returning any values. In order to do that with an arrow function with a body, you need to add a return keyword or better yet just remove the body.

String#match is also probably not the method you're looking for since that returns an array of matches or null if there are no matches. If you use RegExp#test , you will get a boolean depending if the string matches the regular expression.

So maybe the following will suit your needs:

function findFileName(fileName) {
    const detect = (fileName.match(/\.+/g)) ? currentFileExt() : alert("Please enter");
    return detect;

    function currentFileExt() {
        const toArr = fileName.split('');
        const validCharacter = /\.[a-z]+/;
        const fileExtArr = toArr.filter(element => validCharacter.test(element));
        return fileExtArr.join('');
    }
}