Pretty JSON Output

#javascript #webdev #beginners

Tired of the one-liner JSON output, well no more! Utilize JSON.stringify built-in pretty printing. Set the 3rd parameter with your desired spacing level 👍 Bam, instant GLAM✨

const protein = {steak: '🥩', bacon: '🥓'};

JSON.stringify(protein);
// {"steak":"🥩","bacon":"🥓"}

JSON.stringify(protein, null, 2);
/*
{
  "steak": "🥩",
  "bacon": "🥓"
}
*/

Tab Spacing 😉

But the Tab folks are like how about us?? Don’t worry, you can also pass "\t" for tab level spacing 😄

const protein = {steak: '🥩', bacon: '🥓'};

JSON.stringify(protein, null, "\t");

/*
{
    "steak": "🥩",
    "bacon": "🥓"
}
*/

Understanding the "Space" argument

The 3rd parameter of the JSON.stringify is used to control the spacing. It's what gives you that pretty string output.

It allows 2 types of arguments: Number and String.

a. Number

You can use any number from 0 to 10 as your indentation.

const protein = {steak: '🥩', bacon: '🥓'};

JSON.stringify(protein, null, 1);
/*
{
 "steak": "🥩",
 "bacon": "🥓"
}
*/

b. String

Alternatively, you can use a string as your indentation. It allows a maximum of 10 characters. If you try to pass more than 10, it will just use the first 10 characters. So don't try to beat the system 😝

const protein = {steak: '🥩', bacon: '🥓'};

JSON.stringify(protein, null, "I 💛");
/*
{
I 💛"steak": "🥩",
I 💛"bacon": "🥓"
}
*/

What is the 2nd parameter 🤔

The 2nd parameter is also called the replacer parameter. You can use it to transform the result.

It allows 2 types of arguments: Array and Function.

a. Array

I want to show you something really interesting when you pass in an array. You can use it to cherry pick the key-value pair that you want to output.

const protein = {
  steak: '🥩', 
  bacon: '🥓',
  pop: '🥤',
  tea: '🍵',
  shrimp: '🍤',
};

JSON.stringify(protein, ['steak', 'pop'], 2);
/*
{
  "steak": "🥩",
  "pop": "🥤"
}
*/

b. Function

The replacer is called for each item. So you can also pass in a function. This means you can loop over each item and with each pass, manipulate with the logic defined in your function.

Here's an example, where I skip over the properties where the value is not a string. In other words, I only want to show the items where the value is a number.

const protein = {
  steak: '🥩', 
  calorie: 271,
  bacon: '🥓',
  sodium: 58,
};

const replacer = function(key, value) {
  if(typeof value !== "string") {
    return value
  }
  return undefined;
}


JSON.stringify(protein, replacer, 2);
/*
{
  "calorie": 271,
  "sodium": 58
}
*/

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Top comments (8)

Mihail Malo • Jan 28 '19

Doesn't seem like the output of JSON.stringify(protein, null, "I 💛") is recoverable with JSON.parse.

Samantha Ming • Jan 29 '19

oh ya 😮 ...looking into the docs. it seems like:
Throws a SyntaxError exception if the string to parse is not valid JSON.

Definitely something to keep in mind before using the "space" parameter. thanks for catching that!

Mihail Malo • Jan 29 '19 • Edited

I was just curious if there would be a way to recover, for example another parameter you could pass to parse. There isn't though.

const protein = {
  steak: "🥩",
  bacon: "🥓",
  fake: { shrimp: "🍤" },
  array: ["🥩", "🥓", "🍤"]
}
// looks weird but works
JSON.parse(JSON.stringify(protein, null, "\n\t\n\0\r  "))
// SyntaxError
JSON.parse(JSON.stringify(protein, null, "🥓"))

// and my favorite:
// parses as `{sh: "🍤", steak: "🥩", bacon: "🥓"}`
// but breaks nested objects or arrays.
JSON.parse(JSON.stringify({ steak: "🥩", bacon: "🥓" }, null, '"sh":"🍤",'))