See Read and write files in the manual.

Read file

Use readTextFileSync if you don’t want to use await.

Text

  • index.ts 
      const text = await Deno.readTextFile("test.txt");
  console.log(text)

$ deno run --allow-read index.ts

Write file

Use writeTextFileSync if you don’t want to use await.

Text

  • index.ts 
      const output = "Hello, World!";
  const path = "test.txt";

  const write = await Deno.writeTextFile(path, output);

  console.log(`Wrote file: ${path}`);

$ deno run --allow-write index.ts

JSON

Based on example in the docs.

function writeJson(path: string, data: object): string {
  try {
    Deno.writeTextFileSync(path, JSON.stringify(data));

    return console.log(`Wrote file: ${path}`);
  } catch (e) {
    return e.message;
  }
}

const outData = { hello: "World" }
const outPath = "data.json"
console.log(writeJson(outPath, outData));