CSV to SQL

I created this small snippet to convert CSV files to SQL insert statements
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/* eslint-disable */
import { parse } from "csv-parse/sync";

let fileInput = document.createElement('input')
fileInput.type = 'file'
let button = document.createElement("button");
let container = document.createElement("div");
let resultContainer = document.createElement("div");
let idContainer = document.createElement("div");

let targetFiles: FileList

interface Lang<Primitives> {
  formatValue(value: string): Primitives;
  formatColumn(col: string): string;
}

class PSQLLang implements Lang<string | number | boolean> {
  valueRegex = /'/g;
  empty = "null";
  formatValue(value: string) {
    if (!value) return this.empty;
    try {
      let parsed = JSON.parse(value);
      if (typeof parsed === "number") {
        return parsed;
      } else if (typeof parsed === "boolean") {
        return parsed;
      }
    } catch (e) {}
    return `'${value.replace(this.valueRegex, "''")}'`;
  }

  columnRegex = /"/g;
  formatColumn(col: string) {
    return `"${col.replace(this.columnRegex, '\\"')}"`;
  }
}

const langs = {
  psql: new PSQLLang()
};

function cols(columns: string[]) {
  return {
    index: (index: number) => {
      return {
        is: (columnName: any) => columns.indexOf(columnName) === index
      };
    }
  };
}

async function readBlob (blob: Blob) {
  let fr = new FileReader()
  return new Promise(resolve => {
    fr.onload = () => {
      fr.onload = undefined
      resolve(fr.result)
    }
    fr.readAsText(blob)
  })
}

function tryParse(value: string | null) {
  try {
    return JSON.parse(value!);
  } catch {}
}
function getCurrentRequestId() {
  return tryParse(localStorage.getItem("req_id")) || 0;
}

function getNewRequest() {
  let id = getCurrentRequestId();
  id++;
  localStorage.setItem("req_id", JSON.stringify(id));
  return id;
}
idContainer.innerText = "Id: " + getNewRequest();
async function main() {
  let requestId = getNewRequest();

  let text = await readBlob(targetFiles.item(0))
  if (getCurrentRequestId() !== requestId) return;

  const lines = parse(text) as string[][];

  let columnNames = lines.shift()!;
  let columns = cols(columnNames);

  let template =
    `
  INSERT INTO location (${columnNames
    .map((val) => langs.psql.formatColumn(val))
    .join(",")}) 
  VALUES ` +
    lines
      .map(
        (line) =>
          `(${line
            .map((val, i) => {
              let formatted = langs.psql.formatValue(val);
              const col = columns.index(i);
              if (
                (col.is("phone") || col.is("postcode")) &&
                typeof formatted === "number"
              ) {
                return `'${formatted}'`;
              }
              if (
                (col.is("address") || col.is("phone")) &&
                formatted === langs.psql.empty
              ) {
                return "''";
              }
              return formatted;
            })
            .join(", ")})`
      )
      .join(",\n")
      .trim() +
    ";";

  let file = new Blob([template], { type: "text/plain;charset=utf-8" });

  let url = URL.createObjectURL(file);

  let a = document.createElement("a");
  a.href = url;
  a.download = "tmpFile.sql";
  a.innerText = "Download";

  resultContainer.innerHTML = "";
  resultContainer.append(a);

  a.onclick = () => {
    a.remove();
  };
}

container.append(idContainer);
container.append(fileInput)
container.append(button);
container.append(resultContainer);

fileInput.onchange = (e: InputEvent) => {
  let target = e.target as HTMLInputElement
  button.disabled = !target.files.length

  targetFiles = target.files
}

button.textContent = "Run";
button.onclick = () => {
  button.textContent = "Loading";

  main().then(() => {
    button.textContent = "Run";
  });
};

// main();

document.body.innerHTML = "";
document.body.append(container);