Converting array to valid JSON string without using JSON.stringify?

Question

I'm trying to write a function that takes some object, for example a number, a string, a list, or a map (of key-value pairs); and returns a valid JSON representation of that input as a string.

I have already set up other json encoders for simple numbers and string inputs:

Input => Output 
a number with value 123 => 123 (string)
a string with value abc => "abc" (string)

But I'm having issues converting an array such as [1,"2",3]

Input => Output 
1,2,three array => [1,2,"three"] (string)

Here is my current code:

var my_json_encode = function(input) {

  if(typeof(input) === "string"){
      return '"'+input+'"'
  }
  if(typeof(input) === "number"){
      return `${input}`
  }

  //This is causing my issue
  if(Array.isArray(input)) {
      console.log(input)
  }

I could simply add and return JSON.stringify(input) to change it but I don't want to use that. I know I can create some sort recursive solution as I have base cases set up for numbers and strings. I'm blocked on this and any help will be appreciated

Edit: So the solution as been provided below in the answers section! Thanks :)

Note that '"'+input+'"' is not enough to produce valid JSON. Think what will happen if input contains a "... — CherryDT
– CherryDT, Commented Apr 27, 2020 at 20:08

Nina Scholz · Accepted Answer · 2020-04-27 20:00:12Z

1

For arrays take a recursive approach with the items.

const
    json_encode = (input) => {
        if (typeof input === "string") return `"${input}"`;
        if (typeof input === "number") return `${input}`;
        if (Array.isArray(input)) return `[${input.map(json_encode)}]`;
    };

console.log(json_encode([1, 'foo', [2, 3]]));
console.log(JSON.parse(json_encode([1, 'foo', [2, 3]])));

answered Apr 27, 2020 at 20:00

Nina Scholz

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2 Comments

Nina Scholz Over a year ago

you need a check for objects and exclude null in advance. if a value is undefined remove this value.

sisternight438 Over a year ago

So i'm very close to the object and nested object implementation, I've added my code above below the edit. Let me know what I'm missing :)

Pankratiev Alexander · Accepted Answer · 2020-04-27 19:59:37Z

You already have the function that converts scalar values to json values.

So, you can call this function for all array's member (e.g. using https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/Array/map) and then join it (https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/Array/join) and add '[' and ']' to the resulting string

PS: this approach will work also in situations when you have an array of arrays

Example of the implementation:

var my_json_encode = function(input) {

   if(typeof(input) === "string"){
     return '"'+input+'"'
   }
   if(typeof(input) === "number"){
     return `${input}`
   }

   if(Array.isArray(input)) {
      const formatedArrayMembers = input.map(value => my_json_encode(value)).join(',');
      return `[${formatedArrayMembers}]`;
   }
}

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