Vuetify file upload - v-file-input

Dashboard
2

If you add debugger statement in your function, you can clearly see that this.chosenFile is an array

image

FileReader is for a "file"

Adjust your code:

            importTxt() {
                console.log('import')
                if (!this.chosenFile) {
                    this.data = "No File Chosen";
                } else {
                    console.log("File selected");
                    console.log(this.chosenFile);
                    if (!this.chosenFile || this.chosenFile.length !== 1) {
                        console.warn('expected chosenFile to contain 1 item')
                        return
                    }
                    const reader = new FileReader();
                    
                    // Use the javascript reader object to load the contents
                    // of the file in the v-model prop
                    reader.readAsText(this.chosenFile[0]);
                    reader.onload = () => {
                        this.data = reader.result;
                    }
                }
            }

Demo:
chrome_03LhxuCGwh