Javascript JSON stringify()

Introduction

The Javascript JSON.stringify() method converts a JavaScript to a JSON string.

If value has toJSON() method it will call it. 

JSON.stringify(value[, replacer[, space]])
  • value - the value to convert to a JSON string.
  • replacer - Optional, replacer function for the converting.
  • space - Optional, text separator. A number value sets the number of space characters.
let a = JSON.stringify({});
console.log(a);// '{}'
a = JSON.stringify(true);//from www . ja  va2  s  . c o  m
console.log(a);// 'true'
a = JSON.stringify('foo');
console.log(a);// '"foo"'
a = JSON.stringify([1, 'false', false]);
console.log(a);// '[1,"false",false]'
a = JSON.stringify([NaN, null, Infinity]);
console.log(a);// '[null,null,null]'
a = JSON.stringify({ x: 5 });
console.log(a);// '{"x":5}'
a = JSON.stringify(new Date(2020, 0, 2, 15, 4, 5)) 
console.log(a); // '"2020-01-02T15:04:05.000Z"'
a = JSON.stringify({ x: 5, y: 6 });
console.log(a);// '{"x":5,"y":6}'
a = JSON.stringify([new Number(3), new String('false'), new Boolean(false)]);
console.log(a); // '[3,"false",false]'

If value has toJSON() method it will call it. 

let a= JSON.stringify({ x: 5, y: 6, toJSON(){ return this.x + this.y; } });
console.log(a);// '11'

replacer function

The replacer parameter can be either a function or an array.

For a function, it takes two parameters:

  • the key
  • the value. 
function replacer(key, value) {
  if (typeof value === 'string') {
    return undefined;//remove
  }/*from   w w w . ja  v  a 2s.  c o  m*/
  return value;
}

var foo = {
    lang : 'CSS', 
    model: 'client', 
    hours: 45, 
    date: 7
};
let a = JSON.stringify(foo, replacer);
console.log(a);

If replacer is an array, it indicates the names of the properties to include in the resulting JSON string. 

var foo = {/*from   w ww .j  a va 2 s.c o m*/
    lang : 'CSS', 
    model: 'client', 
    hours: 45, 
    date: 7
};

let a = JSON.stringify(foo, ['lang', 'date']);  
console.log(a);

space argument

The space argument can control spacing in the string returned. 

let a = JSON.stringify({ a: 2 }, null, ' ');
console.log(a);

Using a tab character mimics standard pretty-print appearance: 

let a = JSON.stringify({ id: 1, value: 2 }, null, '\t');
console.log(a);



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