Simple way to write JSON to file

Introduction

NodeJS gives us a nice API to write text to files. You can write whatever data you want to a file using fs.writeFile function.

Simple example for text

Write “hello” to a file.

var fs = require("fs");
var fileContent = "hello";

fs.writeFile("./sample.txt", fileContent, (err) => {
    if (err) {
        console.error(err);
        return;
    };
    console.log("File has been created");
});

// Content of the file -> hello

Simple example to write object

Let try to write an object from javascript into a json file. One thing for sure we know is that we have to JSON.stringify the object to make sure its a string before its written.

var fs = require("fs");
var sampleObject = {
    a: 1,
    b: 2,
    c: {
        x: 11,
        y: 22
    }
};

fs.writeFile("./object.json", JSON.stringify(sampleObject), (err) => {
    if (err) {
        console.error(err);
        return;
    };
    console.log("File has been created");
});

// Content of the file -> {"a":1,"b":2,"c":{"x":11,"y":22}}

Correct way to write beautified JSON file

Problem with the above example is that json file is written correctly but its not readable since everything is minified into one line. We never indented for the JSON to be minified this way.

var fs = require("fs");
var sampleObject = {
    a: 1,
    b: 2,
    c: {
        x: 11,
        y: 22
    }
};

fs.writeFile("./object.json", JSON.stringify(sampleObject, null, 4), (err) => {
    if (err) {
        console.error(err);
        return;
    };
    console.log("File has been created");
});

/*
 Content of the file:
 {
     a: 1,
     b: 2,
     c: {
         x: 11,
         y: 22
     }
 } 
 */

Conclusion

Make sure you make use of the space, 3rd optional parameter for the JSON.stringify method. Possible values can be any number or String.

A String or Number object that’s used to insert white space into the output JSON string for readability purposes. If this is a Number, it indicates the number of space characters to use as white space; this number is capped at 10 if it’s larger than that. Values less than 1 indicate that no space should be used. If this is a String, the string (or the first 10 characters of the string, if it’s longer than that) is used as white space. If this parameter is not provided (or is null), no white space is used. ¹

References

1. MDN ↩