JSON stringify
Well known JavaScript method for transforming objects or values into string. However, there is an optional second parameter to the call - a replacer. Once provided, alters the stringification process.
Method
If a method is provided, will be applied to each property of an object. Very handy tool if serialised form has to have for example different values. For example:
let data = {'one' : 1, 'two' : 'a string'};
JSON.stringify(data, (key, value) => key === 'one' ? 2 : value)
// "{"one":2,"two":"a string"}"
As the object being serialized is also available (as this reference), we may perform a wider range of transformations, for example:
data = {x : 1, y : 2, multiplier : 10};
function replacer(key, value) {return typeof value === 'number' ? value * this.multiplier : value}
JSON.stringify(data, replacer);
// "{"x":10,"y":20,"multiplier":100}"
Array
Simply put - a whitelist. Only selected properties will appear in the serialised form. For example:
let data = {'one' : 1, 'two' : 'a string', 'garbage' : 'some'};
JSON.stringify(data, ['one' ,'two']);
// "{"one":1,"two":"a string"}"
To sum up - a very handy tool for quick-and-dirty processing of a bare JSON / JS objects.
Full reference here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
