Identifying the source object when using JSON.stringify

Question

Identifying the source object when using JSON.stringify

There is an object set up like this:

{
  item1: "value1",
  item2: "value2",
  item3: { 
      item4: "value4",
      item5: "value5" 
  }
}

The goal is to utilize JSON.stringify along with a replacer function that behaves differently for items 4 & 5, which are the inner properties of item3.
How can this be achieved?

A hypothetical approach could look something like the code below:

     return JSON.stringify(obj, (key, val) => {
         if (key is child of Item3) {
             return someOtherValue;
         } else {
             return val; 
         } 
}

The expected output in json format would be:

{ 
  "item1" : "value1", 
  "item2" : "value2", 
  "item3" : { 
      "item4" : "theSomeOtherValue", 
      "item5" : "theSomeOtherValue"
}

Edit:
Items 4 & 5 are dynamically generated and not known in advance. Only the title for item3 is known at runtime.

javascript json stringify

Answer 1

Answer №1

When tackling this issue, you have a couple of options available.

Within the replacer function, the object being processed is represented by this. Therefore, when handling item4 and item5, this pertains to the item3 object. If there are distinguishing characteristics of that object, they can be identified based on this. It's important to utilize a conventional function instead of an arrow function so that JSON.stringify is able to define what this refers to during the replacer call.
The replacer function receives the key and value being processed, so if the key of the object ("item3") is unique, special processing can be done when encountering it.

Here are a few examples for approach #1:

For example, if you possess a reference to the object, you can compare this to obj.item3:

const obj = {
    item1: "value1",
    item2: "value2",
    item3: { 
        item4: "value4",
        item5: "value5" 
    }
};
console.log(JSON.stringify(obj, function(key, value) {
//                              ^^^^^^^^^−−−−− Traditional function, not arrow function
    if (this === obj.item3) {
        console.log("do something different, it's " + key);
        return "theSomeOtherValue";
    }
    return value;
}));

If you do not possess a direct reference, any other identifying information about it can be used. For instance, with the given data, it's evident that it includes properties like item4 and item5:

console.log(JSON.stringify({
    item1: "value1",
    item2: "value2",
    item3: { 
        item4: "value4",
        item5: "value5" 
    }
}, function(key, value) {
// ^^^^^^^^^−−−−− Traditional function, not arrow function
    if (this.hasOwnProperty("item4") && this.hasOwnProperty("item5")) {
        console.log("do something different, it's " + key);
        return "theSomeOtherValue";
    }
    return value;
}));

These are just two illustrative cases; the key point is that this represents the object undergoing stringification.

As for approach #2, here's an instance:

console.log(JSON.stringify({
    item1: "value1",
    item2: "value2",
    item3: { 
        item4: "value4",
        item5: "value5" 
    }
}, (key, value) => { // It's okay if this one is an arrow function, we're not relying on
                     // `JSON.stringify` setting `this` for us
    if (key === "item3") {
        return {
            item4: "theSomeOtherValue",
            item5: "theSomeOtherValue"
        };
    }
    return value;
}));

If the entire path of the object under process is required, it may involve additional complexity but can be achieved as follows:

let paths = new Map();
console.log(JSON.stringify({
    item1: "value1",
    item2: "value2",
    item3: { 
        item4: "value4",
        item5: "value5" 
    },
    item6: {
        item3: {
            item4: "non-special item4",
            item5: "non-special item5"
        }
    }
}, function(key, value) {
// ^^^^^^^^^−−−−− Traditional function, not arrow function
    const path = paths.get(this);
    // Special processing for the properties of root.item3
    if (path === "root.item3") {
        return key === "item4" || key === "item5"
            ? "theSomeOtherValue"
            : value;
    }

    // Keep track of the path of the object
    for (const [k, v] of Object.entries(this)) {
        if (typeof v === "object") {
            if (path) {
                // The regex checks for property names that aren't valid(ish)
                // property names so we can use brackets notation
                paths.set(v, path + (/^\w+$/.test(k) ? "." + k : `[${JSON.stringify(k)}]`));
            } else {
                paths.set(v, "root");
            }
        }
    }
    return value;
}));

Answer 2

When tackling this issue, you have a couple of options available.

Within the replacer function, the object being processed is represented by this. Therefore, when handling item4 and item5, this pertains to the item3 object. If there are distinguishing characteristics of that object, they can be identified based on this. It's important to utilize a conventional function instead of an arrow function so that JSON.stringify is able to define what this refers to during the replacer call.
The replacer function receives the key and value being processed, so if the key of the object ("item3") is unique, special processing can be done when encountering it.

Here are a few examples for approach #1:

For example, if you possess a reference to the object, you can compare this to obj.item3:

const obj = {
    item1: "value1",
    item2: "value2",
    item3: { 
        item4: "value4",
        item5: "value5" 
    }
};
console.log(JSON.stringify(obj, function(key, value) {
//                              ^^^^^^^^^−−−−− Traditional function, not arrow function
    if (this === obj.item3) {
        console.log("do something different, it's " + key);
        return "theSomeOtherValue";
    }
    return value;
}));

If you do not possess a direct reference, any other identifying information about it can be used. For instance, with the given data, it's evident that it includes properties like item4 and item5:

console.log(JSON.stringify({
    item1: "value1",
    item2: "value2",
    item3: { 
        item4: "value4",
        item5: "value5" 
    }
}, function(key, value) {
// ^^^^^^^^^−−−−− Traditional function, not arrow function
    if (this.hasOwnProperty("item4") && this.hasOwnProperty("item5")) {
        console.log("do something different, it's " + key);
        return "theSomeOtherValue";
    }
    return value;
}));

These are just two illustrative cases; the key point is that this represents the object undergoing stringification.

As for approach #2, here's an instance:

console.log(JSON.stringify({
    item1: "value1",
    item2: "value2",
    item3: { 
        item4: "value4",
        item5: "value5" 
    }
}, (key, value) => { // It's okay if this one is an arrow function, we're not relying on
                     // `JSON.stringify` setting `this` for us
    if (key === "item3") {
        return {
            item4: "theSomeOtherValue",
            item5: "theSomeOtherValue"
        };
    }
    return value;
}));

If the entire path of the object under process is required, it may involve additional complexity but can be achieved as follows:

let paths = new Map();
console.log(JSON.stringify({
    item1: "value1",
    item2: "value2",
    item3: { 
        item4: "value4",
        item5: "value5" 
    },
    item6: {
        item3: {
            item4: "non-special item4",
            item5: "non-special item5"
        }
    }
}, function(key, value) {
// ^^^^^^^^^−−−−− Traditional function, not arrow function
    const path = paths.get(this);
    // Special processing for the properties of root.item3
    if (path === "root.item3") {
        return key === "item4" || key === "item5"
            ? "theSomeOtherValue"
            : value;
    }

    // Keep track of the path of the object
    for (const [k, v] of Object.entries(this)) {
        if (typeof v === "object") {
            if (path) {
                // The regex checks for property names that aren't valid(ish)
                // property names so we can use brackets notation
                paths.set(v, path + (/^\w+$/.test(k) ? "." + k : `[${JSON.stringify(k)}]`));
            } else {
                paths.set(v, "root");
            }
        }
    }
    return value;
}));

Answer 3

Answer №2

One way to handle the discovered desired object is to save it in a closure and adjust the output based on that object.

This method does not require the use of this.

function updater(parent) {
    let reference = {};
    return function (key, val) {
        if (key === parent) reference = val;
        return key in reference
            ? '#' + val
            : val; 
    };
}

var data = { item1: "value1", item2: "value2", item3: { item4: "value4", item5: "value5" } },
    jsonData = JSON.stringify(data, updater('item3'));

console.log(jsonData);

Answer 4

One way to handle the discovered desired object is to save it in a closure and adjust the output based on that object.

This method does not require the use of this.

function updater(parent) {
    let reference = {};
    return function (key, val) {
        if (key === parent) reference = val;
        return key in reference
            ? '#' + val
            : val; 
    };
}

var data = { item1: "value1", item2: "value2", item3: { item4: "value4", item5: "value5" } },
    jsonData = JSON.stringify(data, updater('item3'));

console.log(jsonData);

Answer 5

Answer №3

When using JSON.stringify, you can include a replacer function as the second argument. This function accepts both the key and value parameters, allowing you to customize the output based on specific conditions.

return JSON.stringify(obj, function(key, val) {
    if (this === obj.item3) {
        return "theSomeOtherValue";
    }
    return val;
});

Alternatively, you can achieve similar results by referencing the current key instead of using this:

return JSON.stringify(obj, function(key, val) {
    if (key === "item4" || key === "item5") {
        return "theSomeOtherValue";
    }
    return val;
});

Answer 6

When using JSON.stringify, you can include a replacer function as the second argument. This function accepts both the key and value parameters, allowing you to customize the output based on specific conditions.

return JSON.stringify(obj, function(key, val) {
    if (this === obj.item3) {
        return "theSomeOtherValue";
    }
    return val;
});

Alternatively, you can achieve similar results by referencing the current key instead of using this:

return JSON.stringify(obj, function(key, val) {
    if (key === "item4" || key === "item5") {
        return "theSomeOtherValue";
    }
    return val;
});

Identifying the source object when using JSON.stringify

Answer №1

Answer №2

Answer №3

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