Tips for saving a JavaScript function in JSON format

Looking to store a JS object in Local Storage for future reference, but struggling to convert it to a string.

Here’s the code:

JSON.stringify({
    x: 10,
    y: function (input) {
        return input;
    }
})

As a result, I get:

"{"x":10}"

Any suggestions on how to save it for later use without using JSON?

(And developing my own Lexer-Parser to handle string functions doesn’t seem feasible)

Answer №1

Here is a suggestion that I believe could be helpful:

Keep your arguments and function body stored in json format:

{"function":{"args":"x,y,z","body":"return x*y+z;"}}

Next, parse the json data and create an instance of the function:

var func = new Function(function.args, function.body);

I believe this method is secure

Answer №2

Typically, when faced with a question like this, it often points to an X/Y dilemma: You are trying to achieve X, you believe Y is the solution, so you attempt Y and then seek help on how to make Y work. In such cases, it might be more beneficial to inquire about how to accomplish X directly.

Addressing the specific query at hand: One potential approach is to utilize replacer and reviver functions to transform the function into a string (during stringify) and back into a function (during parse) in order to store a string representation of the function. However, there are several concerns associated with this method, particularly the scope in which the function is defined which can significantly impact its behavior. Furthermore, converting a string from local storage into executable code involves trusting that the content in local storage has not been tampered with maliciously, posing a security risk to consider.

Although provided below is an example illustrating this technique, I do not recommend employing it unless all other alternatives have been exhausted, primarily due to its reliance on eval, which can introduce vulnerabilities:

// Object containing a function
var obj = {
    a: 5,
    b: function (param) {
        return param;
    }
};

// Converting to JSON utilizing a replacer function
var json = JSON.stringify(obj, function(key, value) {
  if (typeof value === "function") {
    return "/Function(" + value.toString() + ")/";
  }
  return value;
});

// Converting back to an object using a reviver function
var obj2 = JSON.parse(json, function(key, value) {
  if (typeof value === "string" &&
      value.startsWith("/Function(") &&
      value.endsWith(")/")) {
    value = value.substring(10, value.length - 2);
    return (0, eval)("(" + value + ")");
  }
  return value;
});
document.body.innerHTML = obj2.b(42);

The expression (0, eval)("(" + value + ")"); ensures that eval operates at global scope rather than within the reviver function's scope. Normally, eval inherits the scope where it is called, but indirect eval as demonstrated (or by assigning eval to a variable before execution) runs at a global level.

Answer №3

Storing functions in JSON is not allowed.

JSON can only contain values such as string, number, object, array, true, false, or null:

https://i.sstatic.net/RV35n.gif

For more information, visit the official site for JSON at this link.

Answer №4

Here is a straightforward method to achieve this:

let dataString = JSON.stringify( { key1: value1
                           , key2: x => x
                           }
                         , (key, value) => typeof value === "function" ? "" + value : value
                         );

Answer №5

My current approach involves saving the function name and parameter values in an array. The first item in the array is the function name preceded by a $, distinguishing it from regular arrays.

{
    "object": {
        "your-function": ["$functionName", "param-1", "param-2"],
        "color": ["$getColor", "brand", "brand-2"],
        "normal-array": ["normal", "array"]
        ...
    }
}

In this example, I have Sass and JS functions for fetching color values from a global map/object. Extracting the function like this requires tailored code, but I find this method of "storing" functions in JSON quite effective.

Answer №6

I have developed custom functions called JSON.parseIt() and JSON.stringifyIt() following the initial answer, but without relying on the use of eval.

JSON.stringifyIt = (obj)=>{
    return(
        JSON.stringify(obj, function(key, value) {
            if (typeof value === "function") {
                return "/Function(" + value.toString() + ")/";
            }
            if(typeof value === "string"){
                return "/String(" + value.toString() + ")/"
            }
            return value;
        })
    )
}
JSON.parseIt=(json)=>{
    return(
        JSON.parse(json, function(key, value) {
            if (typeof value === "string" &&
            value.startsWith("/Function(") &&
            value.endsWith(")/")) {
                value = value.substring(10, value.length - 2);
                var string = value.slice(value.indexOf("(") + 1, value.indexOf(")"));
                if(/\S+/g.test(string)){
                    return (new Function(string,value.slice(value.indexOf("{") + 1, value.lastIndexOf("}"))))

                }else{
                    return (new Function(value.slice(value.indexOf("{") + 1, value.lastIndexOf("}"))));
                }
                
            }
            if (typeof value === "string" &&
            value.startsWith("/String(") &&
            value.endsWith(")/")){
                value = value.substring(8, value.length - 2);
            }
            return value;
        })
    )
}

// DEMO

var obj = {
    string:"a string",
    number:10,
    func:()=>{
        console.log("this is a string from a parsed json function");
    },
    secFunc:(none,ntwo)=>{console.log(none + ntwo)} ,
    confuse:"/Function(hello)/"
}
const stringifiedObj = JSON.stringifyIt(obj);
console.log("the stringified object is: ",stringifiedObj);

const parsedObj = JSON.parseIt(stringifiedObj);

// console.log("the parsed object is:  ",parsedObj);
console.log(parsedObj.string);
console.log(parsedObj.number);
console.log(parsedObj.confuse);
parsedObj.func();
parsedObj.secFunc(5,6);

The issues I addressed were:

  • Eliminated the use of eval.
  • Corrected an issue in the process of stringifying and parsing, ensuring that a string like "/Function(hello)/" does not become a function when parsed
  • Separated into two distinct functions
  • Implemented parameter insertion

Answer №7

If there is a need to include function definitions in JSON for any specific reason, the following code may be helpful, although it could be slow depending on the size of the object:

function ConvertObjectToJsonWithFunctions(obj, spacing = null) {
    var funcList = {}
    var funcIndex = 0;

    var replaceFuncs = function(key, value) {
        if (typeof value === 'function') {
            funcIndex++;
            var functionName = `___func${funcIndex}___`;
            var functionText = '' + value;
            
            funcList[functionName] = functionText
            
            return functionName;
        }
        
        return value;
    }

    var rawJson = JSON.stringify(obj, replaceFuncs, spacing);

    for (func in funcList) {
        var propValue = `'${func}'`;
        rawJson = rawJson.replace(propValue, funcList[func])
    }

    return rawJson;
}

This code will handle the regular conversion to JSON format. In case of functions, the default stringify method would return them as strings like: "property":"function()...". The code mentioned above creates placeholders (e.g.: "property":"fn1") and maintains a list of functions. Subsequently, it replaces each placeholder with the original function body.

Answer №8

If you are familiar with the keys that can operate as functions, then this script will function properly.

const functionKeys = [ '$alpha', '$omega' ]


const str = JSON.stringify({
  heart: 'soul',
  $alpha ({ one }) {
    console.log(one)
  },
  $omega: function ({ one, two }) {
    console.log(one, two)
  },
  nested: {
    $alpha: function $alpha({ one }) {
      console.log(one)
    },
    $omega: ({ one, two }) => {
      console.log(one, two)
    },
  }
}, onStringify)


const parsed = JSON.parse(str, onParse)

console.log('parsed', parsed)
parsed.$alpha({ one: 'faith' })
parsed.$omega({ one: 'light', two: 'and love' })
parsed.nested.$alpha({ one: 'helios and vesta' })
parsed.nested.$omega({ one: 'knowledge', two: 'is power' })


function onStringify (_, value) {
  return (typeof value === 'function') ? value.toString() : value
}


function onParse (key, value) {
  let formatted = value

  if (functionKeys.includes(key)) {
    const paramsStart = value.indexOf('(') + 1
    const paramsEnd = value.indexOf(')')

    const bodyStart = value.indexOf('{', paramsEnd) + 1
    const bodyEnd = value.lastIndexOf('}')

    formatted = Function(value.substring(paramsStart, paramsEnd), value.substring(bodyStart, bodyEnd))
  }

  return formatted
}

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Improving conditional rendering in Mui <Cards> component by fixing state behavior

I have a situation where I want to display a Floating Action Button inside each Mui card when hovered over. However, I'm running into an issue with the hover state affecting all cards instead of just the one being interacted with. How can I ensure tha ...

"Enhancing the speed of the JavaScript translate function when triggered by a scroll

I am facing an issue with setting transform: translateY(); based on the scroll event value. Essentially, when the scroll event is triggered, #moveme disappears. For a live demonstration, please check out this fiddle: https://jsfiddle.net/bo6e0wet/1/ Bel ...

Turn off logging functionality in a Node.JS environment

I am looking to turn off logging for specific environments in my Node.JS application using Express. Would the following method be considered the most optimal way to disable logging within Node.JS applications? if(process.env.NODE_ENV == "production") { ...

What is the process for extracting components from a JSON file using an observable in Angular?

Take a look at this snippet of code: response: any; fetchData(url: any) { this.response = this.http.get(url); } ngOnInit(): void { fetchData("url.com/data.json"); console.log(this.response) } When I check the console, I see Obser ...

From creating a simple jQuery fiddle, let's delve into the world

Here is a code snippet I'm trying to transition from jQuery to an Angular directive. Visit this link to view the original code: http://jsfiddle.net/rhtr1w04/ Below is my implementation in app.js: angular.module('app',[]).directive('an ...

Ways to enhance background removal in OpenCV using two images

I am currently using OpenCV in conjunction with NodeJS (opencv4nodejs), and I am working on a project that involves replacing the background of webcam images. I have one image with a person's head in the frame, and another without. My code is functio ...

How can I create a placeholder in semantic-ui components?

I'm currently utilizing the plugin and facing an issue with displaying the placeholder. Although data retrieval from the database is functioning properly, the placeholder is not being shown. Note:- When I remove the PHP code, the placeholder display ...

Can one convert to a boolean array in php?

I have a PHP script that I am sending data from JSON in serialized form using JQuery. PHP sees the POST data as a single associative array, which is really convenient. My question is, can I convert this data into a boolean array in PHP? And in general, is ...

What methods are available for updating the href color of an element using the DOM?

I am looking to update the color of a tab (Mathematics-tab) based on the value of 'aria-selected' changing to true in Bootstrap. I have multiple tabs, including one for mathematics, and I want to visually differentiate between selected and unsele ...

Requires a minimum of two page refreshes to successfully load

Our website is currently hosted on Firebase. However, there seems to be an issue as we have to refresh the website at least twice in order for it to load when visiting www.website.com. Update: We are unsure of what could be causing this problem. W ...

Tabulator: the process of loading an extensive amount of data requires a significant amount of time

Currently, I am encountering an issue with loading data using a tabulator on my webpage. There are 38 tables that need to be populated, each containing approximately 2000 rows of data. The problem lies in the fact that it is taking an excessive amount of t ...

The data type 'string[]' cannot be assigned to the data type 'listData[]'

I'm currently developing a flexible component that allows the list view to be utilized by different components. However, the challenge arises from the fact that each component has a different data format. In my project, I'm unable to use type any ...

Pusher authentication issue: socket ID not defined

I am currently facing an issue while trying to establish a private channel for users to transmit data to my node.js server. Upon making the request, I encounter an error where pusher:subscription_error is returned with the error code 500. Upon checking my ...

When utilizing div.load, jQuery and other JavaScript sources may not be defined

When you load a page using jQuery load: $("#myDiv").load("page.php",{foo: bar}); The head section is included in the index: <head> <script src="/assets/plugins/jQuery/jQuery-2.1.4.min.js"></script> <script src="/assets/plugi ...

What's the issue with reducers receiving a Function instead of an Object in Redux?

I encountered an error in my react and redux project but I am unable to figure out how to fix it. Here is the error message: The reducer received unexpected type "Function" as the previous state. It was expecting an object with keys: "posts", "sidebar" ...

Creating tube-like geometry in intervals using three.js

Is there a way in Tube Geometry(Three.js) to plot and render only a portion of the tube at a time, with the option to continue plotting from that point after a set interval or timer? ...

When utilizing DomSanitizer, Angular2 suddenly ceases to function properly

I've been working with Angular 2 and TypeScript. Everything was going well until I encountered an issue with my pipe, which is causing the DomSanitizer to interfere with the (click) event functionality. Even though the (click) code appears intact in ...

Determine the difference between the final value and the second-to-last value within an array

Is there a way to retrieve documents from MongoDB by performing a calculation on two items stored in an array within each document? Specifically, I am interested in fetching all documents where the last item in an array is lower than the second-to-last it ...

Invoke a JSP page using JavaScript

Hello, I'm new to web development and I have a question about calling JSP from a JavaScript file. My project consists of an html file with JavaScript (home.html) and a JSP file (login.jsp). In the home.html file, there are 2 textboxes and 2 buttons - ...

Identifying and detecting Label IDs when clicked using the for tag

I am facing an issue with labels and input fields in my code. I have multiple labels that trigger the same input field, but I want to know which specific label triggered the input field. <label id="label1" for="input1">Document1</label> <la ...