Why does JS concat method with foreach return empty string?

Question

Newbie here so please excuse the ignorance. I wanted to know why my resulting variable is an empty string, when I loop through the array using forEach and concat method.

const concatSpeakersText = arr => {
    const speakerOneText = ''
    const speakerTwoText = ''

    arr.forEach(utterance => {
        utterance.speaker === '1' ? speakerOneText.concat(' ', utterance.text) : speakerTwoText.concat(' ', utterance.text)
    })

    console.log(speakerOneText)
    console.log(speakerTwoText)
}

Strings are immutable. concat() returns a new string, you need to assign it back to the variable. — Barmar
– Barmar, Commented Mar 10, 2021 at 22:22
Duplicate of String Concat not working in scope JS. Read the documentation of concat. This has nothing to do with forEach. You could’ve reduced your minimal reproducible example to let str = ""; str.concat("string"); console.log(str);. — Sebastian Simon
– Sebastian Simon, Commented Mar 10, 2021 at 22:25

Nina Scholz · Accepted Answer · 2021-03-10 22:25:45Z

1

You need to assign to a variable with String#concat or take an object with the speakers.

const concatSpeakersText = arr => {
    const speakers = { speakerOneText: '', speakerTwoText: '' };

    arr.forEach(utterance => {
        speakers[utterance.speaker === '1'
            ? 'speakerOneText'
            : 'speakerTwoText'
        ] += ' ' + utterance.text;
    });

    console.log(speakers.speakerOneText)
    console.log(speakers.speakerTwoText)
}

answered Mar 10, 2021 at 22:25

Nina Scholz

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