Cloning a json object and changing values mutates the original object as well

Question

I was wondering why does this happen?

I have an json object stored in var myObj:

var myObj = JSON.parse(fs.readFileSync(\'json/data.json\', \'utf8\')         


        

Answer 1

although JSON.parse(JSON.stringify(myObj)) may seem simple and tempting, especially for bigger data structures it is not, because it has to serialize the objects and then parse this string again. I'd reccomend something like this:

function clone(deep, obj=undefined){
    var fn = clone[deep? "deep": "shallow"] || function(obj){
        return (!obj || typeof obj !== "object")? obj:  //primitives
            Array.isArray(obj)? obj.map(fn):            //real arrays
            deep? 
                //make a deep copy of each value, and assign it to a new object;
                Object.keys(obj).reduce((acc, key) => (acc[key] = fn(obj[key]), acc), {}):
                //shallow copy of the object
                Object.assign({}, obj);
    };
    return obj === undefined? fn: fn(obj);
}
clone.deep = clone(true);
clone.shallow = clone(false);

and then

//make a deep copy
var modObj = clone.deep(myObj);
//or 
var modObj = clone(true, myObj);

//or a shallow one
var modObj = clone.shallow(myObj);
//or
var modObj = clone(false, myObj);

I prefer this style clone.deep(whatever) because the code is self explaining and easy to scan over.