I have implemented such a code. I only want to throw one key into the array under the name ("args"). Unfortunately my code returns in line 91 "TypeError: Cannot read properties of undefined (reading 'length')". How to fix it?
All is into async function :)
var objmapPolygon = {}, objmapBsc = {};
let jsonValueBsc = JSON.parse(fs.readFileSync('eventsBsc.json'));
let jsonValuePolygon = JSON.parse(fs.readFileSync('eventsPolygon.json'));
var mapped = jsonValuePolygon.map(
function (v) { for (var l in v) {this[l] = v[l];} },
objmapPolygon
);
console.log(objmapPolygon)
var mapps = jsonValueBsc.map(
function (v) { for (var l in v) {this[l] = v[l];} },
objmapBsc
);
console.log(objmapBsc)
const resultPolygon = mapps.filter(mapp => mapp.length < 7);
console.log(resultPolygon);
The .map() function returns an array filled with the values returned from the callback function. Your jsonValueBsc.map callback function does not return anything, so it is an array of the default return value undefined. When you access those array elements in mapps.filter(mapp => mapp.length < 7), mapp is undefined, thus you get an error.
Return something from the first mapping so there is a value, preferably an array so .length is meaningful.
below is one piece of code where i have to compare one object stored value (i.e 'resort') with the value compare that value what i am getting from the JSON file .
code -
resort = _.find(this.resorts.entries, (o) => {
return o.gqe_name === resort;
})
;
i have tried to get the value but the it is displaying as [Object,Object ] , tried with console .log('resort'+ resort) and log.info ('resort'+ resort).
is there any way i can view the return value ?
how i can print json stored value 'o.gqe_name' ?
JSON.stringify can help
const object = { test: { test2: 'value' } }
const result = JSON.stringify(object)
const result2 = JSON.stringify(object, null, 2)
console.log(result)
console.log(result2)
I am making a discord bot where you can use the command tcp freeitem to obtain your free item.
I am trying to alter that value of an Account by adding a new item object into the account. When I map the array to replace a value, it erases the name (allAccounts) of the array of the json. More information below. Here is what I have:
const listOfAllItemNames = require(`C:/Users///censored///OneDrive/Desktop/discord bot/itemsDataList.json`)
const accountList = require(`C:/Users///censored///OneDrive/Desktop/discord bot/account.json`)
const fs = require('fs')
var accountThatWantsFreeItem = accountList.allAccounts.find(user => message.author.id === user.userId);
var randomFreeItem = listOfAllItemNames.allItems[Math.floor(Math.random() * listOfAllItemNames.allItems.length)]
if(accountThatWantsFreeItem === undefined) {message.reply('You need to make an account with tcp create!'); return; }
if(accountThatWantsFreeItem.freeItem === true) {message.reply('You already got your free one item!'); return;}
fs.readFile('C:/Users///censored///OneDrive/Desktop/discord bot/account.json', 'utf8', function readFileCallback(err,data) {
if(err){
console.error(err)
} else {
var accountsArray = JSON.parse(data)
console.log(accountsArray)
var whoSentCommand = accountsArray.allAccounts.find(user => message.author.id === user.userId)
whoSentCommand.Items.push(randomFreeItem)
whoSentCommand.freeItem = true;
var test = accountsArray.allAccounts.map(obj => whoSentCommand === obj.id || obj)
//I believe the issue is trying to map it returns a new array
console.log(test)
test = JSON.stringify(test, null, 5)
//fs.writeFile('C:/Users///censored///OneDrive/Desktop/discord bot/account.json', test, err =>{ console.error(err)} )
}
})
when I write the file back to json file, it removes the "allAccounts" identifier in this file
//json file
//array name "allAccounts" is removed, I need this still here for code to work
{
"allAccounts" : [
{
"userId": "182326315813306368",
"username": "serendipity",
"balanceInHand": 0,
"balanceInBank": 0,
"freeItem": false,
"Items": []
},
(No "allAccounts" array name)
to this: output after writing file
So, the final question is
How would I alter the array so that I only alter the account I want without editing the array name?
Please feel free to ask any questions if I was unclear.
Array.map() method returns the converted array.
So in the below line, map() method takes allAccounts array and perform actions and put the target array (not object) to the test variable.
var test = accountsArray.allAccounts.map(obj => whoSentCommand === obj.id || obj)
So for making code works, please change the code like this:
var test = {
"accountsArray": accountsArray.allAccounts.map(obj => whoSentCommand === obj.id || obj)
}
When posting questions, please please reduce the code to a minimal example that will demonstrate the problem, and use words, not code, to describe the problem.
It looks like you are expecting .map to do something other than what it does.
Please consult the documentation for Array.map().
It takes the array that you pass it (in this case accountsArray.allAccounts) and transforms it, returning the transformed array.
You have essentially done test = accountsArray.allAccounts but for some reason are expecting test to contain an Object with the key allAccounts, when in fact it will only contain an Array, because that is what you have assigned it.
Take this object:
x = {
"key1": "xxx",
"key2": function(){return this.key1}
}
If I do this:
y = JSON.parse( JSON.stringify(x) );
Then y will return { "key1": "xxx" }. Is there anything one could do to transfer functions via stringify? Creating an object with attached functions is possible with the "ye goode olde eval()", but whats with packing it?
json-stringify-function is a similar post to this one.
A snippet discovered via that post may be useful to anyone stumbling across this answer. It works by making use of the replacer parameter in JSON.stringify and the reviver parameter in JSON.parse.
More specifically, when a value happens to be of type function, .toString() is called on it via the replacer. When it comes time to parse, eval() is performed via the reviver when a function is present in string form.
var JSONfn;
if (!JSONfn) {
JSONfn = {};
}
(function () {
JSONfn.stringify = function(obj) {
return JSON.stringify(obj,function(key, value){
return (typeof value === 'function' ) ? value.toString() : value;
});
}
JSONfn.parse = function(str) {
return JSON.parse(str,function(key, value){
if(typeof value != 'string') return value;
return ( value.substring(0,8) == 'function') ? eval('('+value+')') : value;
});
}
}());
Code Snippet taken from Vadim Kiryukhin's JSONfn.js or see documentation at Home Page
I've had a similar requirement lately. To be clear, the output looks like JSON but in fact is just javascript.
JSON.stringify works well in most cases, but "fails" with functions.
I got it working with a few tricks:
make use of replacer (2nd parameter of JSON.stringify())
use func.toString() to get the JS code for a function
remember which functions have been stringified and replace them directly in the result
And here's how it looks like:
// our source data
const source = {
"aaa": 123,
"bbb": function (c) {
// do something
return c + 1;
}
};
// keep a list of serialized functions
const functions = [];
// json replacer - returns a placeholder for functions
const jsonReplacer = function (key, val) {
if (typeof val === 'function') {
functions.push(val.toString());
return "{func_" + (functions.length - 1) + "}";
}
return val;
};
// regex replacer - replaces placeholders with functions
const funcReplacer = function (match, id) {
return functions[id];
};
const result = JSON
.stringify(source, jsonReplacer) // generate json with placeholders
.replace(/"\{func_(\d+)\}"/g, funcReplacer); // replace placeholders with functions
// show the result
document.body.innerText = result;
body { white-space: pre-wrap; font-family: monospace; }
Important: Be careful about the placeholder format - make sure it's not too generic. If you change it, also change the regex as applicable.
Technically this is not JSON, I can also hardly imagine why would you want to do this, but try the following hack:
x.key2 = x.key2.toString();
JSON.stringify(x) //"{"key1":"xxx","key2":"function (){return this.key1}"}"
Of course the first line can be automated by iterating recursively over the object. Reverse operation is harder - function is only a string, eval will work, but you have to guess whether a given key contains a stringified function code or not.
You can't pack functions since the data they close over is not visible to any serializer.
Even Mozilla's uneval cannot pack closures properly.
Your best bet, is to use a reviver and a replacer.
https://yuilibrary.com/yui/docs/json/json-freeze-thaw.html
The reviver function passed to JSON.parse is applied to all key:value pairs in the raw parsed object from the deepest keys to the highest level. In our case, this means that the name and discovered properties will be passed through the reviver, and then the object containing those keys will be passed through.
This is what I did https://gist.github.com/Lepozepo/3275d686bc56e4fb5d11d27ef330a8ed
function stringifyWithFunctions(object) {
return JSON.stringify(object, (key, val) => {
if (typeof val === 'function') {
return `(${val})`; // make it a string, surround it by parenthesis to ensure we can revive it as an anonymous function
}
return val;
});
};
function parseWithFunctions(obj) {
return JSON.parse(obj, (k, v) => {
if (typeof v === 'string' && v.indexOf('function') >= 0) {
return eval(v);
}
return v;
});
};
The naughty but effective way would be to simply:
Function.prototype.toJSON = function() { return this.toString(); }
Though your real problem (aside from modifying the prototype of Function) would be deserialization without the use of eval.
I have come up with this solution which will take care of conversion of functions (no eval). All you have to do is put this code before you use JSON methods. Usage is exactly the same but right now it takes only one param value to convert to a JSON string, so if you pass remaning replacer and space params, they will be ignored.
void function () {
window.JSON = Object.create(JSON)
JSON.stringify = function (obj) {
return JSON.__proto__.stringify(obj, function (key, value) {
if (typeof value === 'function') {
return value.toString()
}
return value
})
}
JSON.parse = function (obj) {
return JSON.__proto__.parse(obj, function (key, value) {
if (typeof value === 'string' && value.slice(0, 8) == 'function') {
return Function('return ' + value)()
}
return value
})
}
}()
// YOUR CODE GOES BELOW HERE
x = {
"key1": "xxx",
"key2": function(){return this.key1}
}
const y = JSON.parse(JSON.stringify(x))
console.log(y.key2())
It is entirely possible to create functions from string without eval()
var obj = {a:function(a,b){
return a+b;
}};
var serialized = JSON.stringify(obj, function(k,v){
//special treatment for function types
if(typeof v === "function")
return v.toString();//we save the function as string
return v;
});
/*output:
"{"a":"function (a,b){\n return a+b;\n }"}"
*/
now some magic to turn string into function with this function
var compileFunction = function(str){
//find parameters
var pstart = str.indexOf('('), pend = str.indexOf(')');
var params = str.substring(pstart+1, pend);
params = params.trim();
//find function body
var bstart = str.indexOf('{'), bend = str.lastIndexOf('}');
var str = str.substring(bstart+1, bend);
return Function(params, str);
}
now use JSON.parse with reviver
var revivedObj = JSON.parse(serialized, function(k,v){
// there is probably a better way to determ if a value is a function string
if(typeof v === "string" && v.indexOf("function") !== -1)
return compileFunction(v);
return v;
});
//output:
revivedObj.a
function anonymous(a,b
/**/) {
return a+b;
}
revivedObj.a(1,2)
3
To my knowledge, there are no serialization libraries that persist functions - in any language. Serialization is what one does to preserve data. Compilation is what one does to preserve functions.
It seems that people landing here are dealing with structures that would be valid JSON if not for the fact that they contain functions. So how do we handle stringifying these structures?
I ran into the problem while writing a script to modify RequireJS configurations. This is how I did it. First, there's a bit of code earlier that makes sure that the placeholder used internally (">>>F<<<") does not show up as a value in the RequireJS configuration. Very unlikely to happen but better safe than sorry. The input configuration is read as a JavaScript Object, which may contain arrays, atomic values, other Objects and functions. It would be straightforwardly stringifiable as JSON if functions were not present. This configuration is the config object in the code that follows:
// Holds functions we encounter.
var functions = [];
var placeholder = ">>>F<<<";
// This handler just records a function object in `functions` and returns the
// placeholder as the value to insert into the JSON structure.
function handler(key, value) {
if (value instanceof Function) {
functions.push(value);
return placeholder;
}
return value;
}
// We stringify, using our custom handler.
var pre = JSON.stringify(config, handler, 4);
// Then we replace the placeholders in order they were encountered, with
// the functions we've recorded.
var post = pre.replace(new RegExp('"' + placeholder + '"', 'g'),
functions.shift.bind(functions));
The post variable contains the final value. This code relies on the fact that the order in which handler is called is the same as the order of the various pieces of data in the final JSON. I've checked the ECMAScript 5th edition, which defines the stringification algorithm and cannot find a case where there would be an ordering problem. If this algorithm were to change in a future edition the fix would be to use unique placholders for function and use these to refer back to the functions which would be stored in an associative array mapping unique placeholders to functions.
Is it possible to log variable name (not value) in JavaScript?
var max_value = 4;
console.log(max_value); // should log "max_value" as a string
UPDATE: I need a testing function that should be able to log any variable name (passed as an argument) as a string, not just this one variable.
There is a solution that can help you. I grabbed this function from this stackoverflow answer, which is able to get the name of the function parameters:
var STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;
var ARGUMENT_NAMES = /([^\s,]+)/g;
function getParamNames(func) {
var fnStr = func.toString().replace(STRIP_COMMENTS, '');
var result = fnStr.slice(fnStr.indexOf('(')+1, fnStr.indexOf(')')).match(ARGUMENT_NAMES);
if(result === null)
result = [];
return result;
}
then all you need to do now, is to use the name of your variable as a parameter of an anonymous function and pass all the function as argument of the getParamNames :
variablesNames = getParamNames(function (max_value, min_value) {});
This will return an array like this :
result => ["max_value", "min_value"];
Let's make it practical, first change the name of the getParamNames function to something easy and small like this :
function __ (func) {
// code here ...
}
second thing, instead of returning an array, just return the first element of the array, change this :
return result;
to this :
return result.shift();
now, you can get the name of your variable like this :
__(function( max_value ){});