Why do I get the error<string>.matchAll() is not a function in Node.js v18.15.0?

I am working with regular expressions in Node.js, and I’m trying to match words in a line of text. I’m trying to use matchAll as I want to do something with all words in each line. However, I get the error "TypeError: line.matchAll is not a function" when I call matchAll.

I’ve tried calling matchAll in different ways, wondering if I called it incorrectly (I’m new to Node.js) but that just resulted in other errors. Here’s the relevant section of my code:

const regex = /[a-zA-Z']{2,}/g
var leftOver = '';
var read, line, idxStart, idx;
while((read = fs.readSync(fd, buf, 0, bufSize, null)) !== 0) { 
    leftOver += buf.toString('utf-8', 0, read);
    idxStart = 0;
    while((idx = leftOver.indexOf("\n", idxStart)) !== -1) {
        line = leftOver.substring(idxStart, idx).toLowerCase;
        let wordsInLine = line.matchAll(regex); // this is where I get my error
        for(word of wordsInLine) {
            // do something
        }
        idxStart = idx + 1;
    }
    leftOver = leftOver.substring(idxStart); 
}

I’ve looked for other answers, but everything I’ve seen just says matchAll is only available in Node.js v12.0 up, and that isn’t my issue, as I’m using Node.js v18.

>Solution :

These two statements are the culprit:

line = leftOver.substring(idxStart, idx).toLowerCase;
let wordsInLine = line.matchAll(regex); 

In the first one you set the value of line to be a method. That method being String.prototype.toLowerCase. It is no more a string.

Fix this, by executing the method:

line = leftOver.substring(idxStart, idx).toLowerCase();
let wordsInLine = line.matchAll(regex);