[javascript] Conversion between UTF-8 ArrayBuffer and String

The methods readAsArrayBuffer and readAsText from a FileReader object converts a Blob object to an ArrayBuffer or to a DOMString asynchronous.

A Blob object type can be created from a raw text or byte array, for example.

let blob = new Blob([text], { type: "text/plain" });

let reader = new FileReader();
reader.onload = event =>
{
    let buffer = event.target.result;
};
reader.readAsArrayBuffer(blob);

I think it's better to pack up this in a promise:

function textToByteArray(text)
{
    let blob = new Blob([text], { type: "text/plain" });
    let reader = new FileReader();
    let done = function() { };

    reader.onload = event =>
    {
        done(new Uint8Array(event.target.result));
    };
    reader.readAsArrayBuffer(blob);

    return { done: function(callback) { done = callback; } }
}

function byteArrayToText(bytes, encoding)
{
    let blob = new Blob([bytes], { type: "application/octet-stream" });
    let reader = new FileReader();
    let done = function() { };

    reader.onload = event =>
    {
        done(event.target.result);
    };

    if(encoding) { reader.readAsText(blob, encoding); } else { reader.readAsText(blob); }

    return { done: function(callback) { done = callback; } }
}

let text = "\uD83D\uDCA9 = \u2661";
textToByteArray(text).done(bytes =>
{
    console.log(bytes);
    byteArrayToText(bytes, 'UTF-8').done(text => 
    {
        console.log(text); //  = ?
    });
});

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