Node.js - How to write/serialize an arbitrary JavaScript object that contains functions and special values and save it to a .js file

Question

I have a JavaScript object that contains functions and special values like Infinity, as well as strings and numbers:

const myObject = {
   propertyA: "my string",
   propertyB: 5,
   propertyC: () => "function returing a string",
   propertyD: Infinity
};

I would like to save it to a file so that the resulting content looks like this:

export default function () {
    return {
        propertyA: "my string",
        propertyB: 5,
        propertyC: () => "function returing a string",
        propertyD: Infinity
    };
}

I have tried to use JSON.stringify(), but that doesn't work with functions and special values, as those are not valid JSON:

writeFileSync('my-output.js', `
   export default function () {
       return ${ JSON.stringify(myObject) };
   }
`);

const myObject = {
   propertyA: "my string",
   propertyB: 5,
   propertyC: () => "function returing a string",
   propertyD: Infinity
};

console.log(JSON.stringify(myObject, null, 4));

Is there any other way to do this?

Indeed, functions are not valid JSON but it still valid javascript object and I want to write a javascript file ;) — JoG
– JoG, Commented Sep 8, 2018 at 18:22

Danziger · Accepted Answer · 2018-09-08 21:04:28Z

2

You need a different way to serialize your object other than JSON.stringify, maybe something like this:

// Pretty:

const TAB = '    ';
const BR = '\n';
const CBR = `,${ BR }`;

// Minified: 

// const TAB = '';
// const BR = '';
// const CBR = ',';

function arrayAsString(arr, depth=0) {
  const _ = TAB.repeat(depth - 1);
  const __ = _ + TAB;
  
  return `[${
    BR }${ arr.map(value =>
    `${ __ }${ serialize(value, depth) }`).join(CBR) }${
    BR }${ _ }]`;
}

function objectAsString(obj, depth=0) {
  const _ = TAB.repeat(depth - 1);
  const __ = _ + TAB;
  
  return `{${
    BR }${ Object.entries(obj).map(([key, value]) =>
    `${ __ }${ key }: ${ serialize(value, depth) }`).join(CBR) }${
    BR }${ _ }}`;
}

function serialize(value, depth=0) {
  if (value === null) {
    return `${ value }`;
  } else if (Array.isArray(value)) {
    return arrayAsString(value, depth + 1);
  } else if (typeof value === 'object') {
    return objectAsString(value, depth + 1);
  } else if (typeof value === 'string') {
    return `"${ value }"`;
  } else {
    return `${ value }`;
  }
}

const notStringifyableObject = {
  1: Infinity,
  str: "my string",
  num: 5,
  func: () => console.log('It works! 🎉'),
  mixArr: [{
    value: 1
  }, {
    value: 2
  }, 1, 2, [3, 4, 5]],
  arr: [1, 2, 3],
  obj: { foo: 'bar' },
  nil: null,
  und: undefined
};

const serialized = serialize(notStringifyableObject);

// This is what you would save in a file:
console.log(`export default ${ serialized };`);

// Check if it's actually working: 

eval(`test = ${ serialized }`);

test.func();

.as-console-wrapper {
  max-height: 100vh !important;
}

Then, once you have serialized your object, you can save its string representation to a file with some additional code so that you can later load it using require, as you have already done:

writeFileSync('my-output.js', `export default () => ${ serialized };`);

Or:

writeFileSync('my-output.js', `export default ${ serialized };`);

Note that's just a basic implementation and it doesn't support regular expression, dates, circular structures... So you might prefer to use a library like serialize-javascript or serialize-to-js instead of implementing your own solution.

edited Sep 8, 2018 at 21:04

answered Sep 8, 2018 at 18:42

Danziger

21.4k6 gold badges59 silver badges91 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

JoG Over a year ago

it crash when a value is null

Danziger Over a year ago

@JoG Fixed. That's because typeof null is "object", so there should be a condition that checks and handles that inside serialize().

Collectives™ on Stack Overflow

Node.js - How to write/serialize an arbitrary JavaScript object that contains functions and special values and save it to a .js file

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related