Tips for saving a JavaScript function in JSON format

Question

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)

javascript json

Answer 1

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

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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

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 11

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 12

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 13

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 14

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 15

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
}

Answer 16

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
}

Tips for saving a JavaScript function in JSON format

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

Answer №8

Similar questions

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

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

Turn off logging functionality in a Node.JS environment

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

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

Ways to enhance background removal in OpenCV using two images

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

Can one convert to a boolean array in php?

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

Requires a minimum of two page refreshes to successfully load

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

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

Pusher authentication issue: socket ID not defined

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

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

Creating tube-like geometry in intervals using three.js

When utilizing DomSanitizer, Angular2 suddenly ceases to function properly

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

Invoke a JSP page using JavaScript

Identifying and detecting Label IDs when clicked using the for tag