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.
Today I've faced interesting problem of create test for pretty simple behavior: 'Most recent' sorting. All what test need to know:
Every item have ID
Previous ID is less then next in this case of sorting
Approach: writing ID in to attribute of item, getting that id from first item with getAttribute() and either way for second.
Problem: getAttribute() promise resulting with string value and Jasmine is not able to compare (from the box) string numbers.
I would like to find elegant way to compare them with toBeLessThan() instead of using chains of few .then() that will be finished with comparing that things.
Root of no-type-definition evil
Thanks guys <3
You can create a helper function to convert string number to actual number, which will make use of Promises:
function toNumber(promiseOrValue) {
// if it is not a promise, then convert a value
if (!protractor.promise.isPromise(promiseOrValue)) {
return parseInt(promiseOrValue, 10);
}
// if promise - convert result to number
return promiseOrValue.then(function (stringNumber) {
return parseInt(stringNumber, 10);
});
}
And then use the result with .toBeLessThan, etc:
expect(toNumber(itemId)).toBeLessThan(toNumber(anotherItemId));
I forgot of native nature of promises but tnx to Michael Radionov I've remembered what I want to do.
expect(first.then( r => Number(r) )).toBe(next.then( r => Number(r) ));
I guess this stroke looks simple.
UPDATE
ES6:
it('should test numbers', async function () {
let first = Number(await $('#first').getText());
let second = Number(await $('#second').getText());
expect(first).toBeGreaterThan(second);
})
One option to approach it with a custom jasmine matcher:
toBeSorted: function() {
return {
compare: function(actual) {
var expected = actual.slice().sort(function (a, b) {
return +a.localeCompare(+b);
});
return {
pass: jasmine.matchersUtil.equals(actual, expected)
};
}
};
},
Here the matcher takes an actual input array, integer-sort it and compare with the input array.
Usage:
expect(element.all(by.css(".myclass")).getAttribute("id")).toBeSorted();
Note that here we are calling getAttribute("id") on an ElementArrayFinder which would resolve into an array of id attribute values. expect() itself is patched to implicitly resolve promises.
I'm trying to implement an afterFind hook on a model and can't quite figure out what the semantics are. I'll pulled the following together from trial and error using the doc and other StackOverflow questions as guidelines.
My goal is to massage the result (by applying get(plain : true)) and pass the transformed value as the result of the promise. For instance, I'd expect/want this to return an empty result set:
hooks: {
afterFind: function(result, options, fn)
{
result = [];
}
},
but it just causes the request to hang. Documentation says the arguments are pass by reference and doesn't include a return. Other samples imply something like:
hooks: {
afterFind: function(result, options, fn)
{
result = [];
return fn(null, result);
}
},
which doesn't hang, but doesn't change my result set. Not to mention, I've no idea what the magical "fn" argument is/does.
I had a similar problem. This is because when you do a findAll the argument passed to the hook is an array of values instead of a single object. I did this as a workaround -
hooks: {
afterFind: function(result) {
if(result.constructor === Array) {
var arrayLength = result.length;
for (var i = 0; i < arrayLength; i++) {
result[i].logo = "works";
}
} else {
result.logo = "works";
}
return result;
}
}
In the above code I change the logo attribute of the record(s) after finding it.
I have an issue with CreateAssociation method.
Here's my code :
User create curves
//User create curves
function saveCurves(user, functions){
var curves = JSON.parse(functions);
for (var i = 0; i < curves.length; i++) {
(function(i,user,curves){
user.createCurve({
i_min: curves[i].i_min,
i_max: curves[i].i_max,
}).then(function(curve){
saveFunction(curve,curves[i].fn,curves[i].variables);
});
})(i,user,curves);
}
}
//save function after creating curves depends on it
function saveFunction(curve,fct,variables){
return curve.createFunction({
fn: fct
}).then(function(math_function){
saveVariables(math_function,variables);
return;
})
}
//save variables to associated function
function saveVariables(fn, variables){
for(var j= 0; j < variables.length; j++){
(function(j,fn,variables){
fn.createVariable({
name: variables[j].name,
function_id: fn.id
})
.then(function(row_variable){
console.log(row_variable.toJSON())
return row_variable.createFunction({
fn: variables[j].fn
})
})(j,fn,variables);
}
I have an issue when I'm calling "fn.createVariable" Method.
I don't really understand why but the promise in .then just after give me fn instance instead of variable instance.
and also I have this error :
Unhandled rejection TypeError: row_variable.createFunction is not a function
When i'm looked into my database, I saw the instance has been correctly inserted
but row_variable in console.log give me fn and not inserted row.
So I cannot understand with I have this return.
I did it well above, so why it doesn't work here ?
(Not relation definition issue because row exist in database)
Any idea please ?
This question is about functional tests written with the Intern.
The elementsByXYZ methods returns an array of elements. I've noticed that I'm able to call the method click() on these returned elements, but I cannot for example call the method getAttribute(attributeName).
What is the list of methods that can be called on elements returned by a a elementsByXYZ method ?
Here is a code snippet that illustrates what I'm trying to achieve:
return this.remote
.get(require.toUrl("./testpage.html"))
.waitForCondition('ready', 5000)
.elementById('widget1')
.elementsByTagName('div')
.then(function(children){
assert.equal(7, children.length, 'The expected number of children is wrong');
for(var i=0; i < 7; i++){
console.log(children[i].getAttribute('className'));
children[i].click();
}
});
The console shows that children[i].getAttribute('className') returns undefined, while I can see that the clicks are correctly performed on each child.
Wouldn't you need to use something like:
elem.getAttribute('class', function (err, text) {
console.log(text);
)};
When using wd.js? e.g. https://github.com/admc/wd/blob/master/doc/jsonwire-mapping.md
getAttribute(element, attrName, cb) -> cb(err, value)
That works for me.