Exit function on subfunction result

Exit function on subfunction result - javascript

I wonder if there is a method to exit function based on other function output.
In other words: I have a function that evaluates some values and if they are fine returns them, otherwise causes a warning to user.
const verifier = () => {
const a = Number(document.querySelector("#a").value);
const b = Number(document.querySelector("#b").value);
if(isNaN(a) || isNaN(b)) {
console.log("Sent notification to user");
return
}
return [a, b]
}
Now, I use it multiple times, e.g.:
const adder = () => {
const [a,b] = verifier() || return; // <--- HERE!
console.log(a);
console.log(b);
}
In HERE: if verification function returns false / undefined / null I would like to exit my function prematurely, otherwise: assign to variables.

As I wrote in my comment, if you're willing to introduce an intermediary helper, you could write it as follows:
const verifier = () => {
const a = Number(document.querySelector("#a").value);
const b = Number(document.querySelector("#b").value);
if(isNaN(a) || isNaN(b)) {
console.log("Sent notification to user");
return;
}
return [a, b];
}
// helper that only calls `fn` if verifier does not return undefined
const ifVerified = (fn) => {
const values = verifier();
return undefined === values ? undefined : fn(values);
};
const adder = () => ifVerified(([a, b]) => {
// do something with a and b
});

You can't use return where an expression is expected, because return is a statement.
There are a bunch of other ways to do it, but they're all going to be clunkier than you're going to want. :-) For instance, you could have verifier return the NaN values and then test the result:
const verifier = () => {
const a = Number(document.querySelector("#a").value);
const b = Number(document.querySelector("#b").value);
if (isNaN(a) || isNaN(b)) {
console.log("Sent notification to user");
return [NaN, NaN];
}
return [a, b];
};
const adder = () => {
const [a,b] = verifier();
if (isNaN(a)) {
return;
}
console.log(a);
console.log(b);
};
Or you could leave verifier as it is and use nullish coalescing (quite new) at the point where you call it:
const adder = () => {
const [a, b] = verifier() ?? [];
if (a === undefined) {
return;
}
console.log(a);
console.log(b);
};
perhaps with an explicit flag value as a default:
const adder = () => {
const [a = null, b] = verifier() ?? [];
if (a === null) {
return;
}
console.log(a);
console.log(b);
};
Or store the returned array/undefined and test that:
const adder = () => {
const result = verifier();
if (!result) {
return;
}
const [a, b] = result;
console.log(a);
console.log(b);
};
But they all involve that if. (Or you could throw.)

Related

Recurse in Linked List

I have been practicing the linked list and wanted to implement the recurse on it, although in some cases I was able to implement it efficiently, in other cases I failed miserably at doing so. I would like to know a method to do the recursive so as not to have to use the "while" to go through the Linked List, I have used the recurse to go through the arrays but when I wanted to do it similar in this case it fails.
I don't have much experience in implementing recursion and wanted to apply it in this method to get more experience with it, but at least it helped me understand the Linked List more by having to do it over and over again. Thank you.
class Node {
// Accept arguments (the second one could be optional)
constructor(data, next) {
this.data = data;
this.next = next;
}
lastNode() { // new method that uses recursion
return this.next?.lastNode() || this;
}
}
class ListRecurse {
constructor() {
this.head = null;
this.size = 0;
}
add(data) {
let newNode = new Node(data); // No second argument. It has a default value
if (this.head === null) {
this.head = newNode;
} else {
// The lastNode implementation uses recursion:
this.head.lastNode().next = newNode;
}
this.size ++;
return this; // to allow chaining
}
insertAdd(data, index) {
if (index < 0 || index > this.size) {
return null;
}
let newNode = new Node(data);
let current = this.head;
let prev;
if (index === 0) {
newNode.next = current;
this.head = newNode;
}
else {
for (let i = 0; i < index; i++) {
prev = current;
current = current.next;
}
this.head.lastNode().next = current;
prev.next = newNode;
}
this.size++;
return this;
}
Print() {
if (!this.size) {
return null;
}
let current = this.head;
let result = "";
while(current) {
result += current.data += "=>";
current = current.next;
}
result += "X";
return result;
}
DeletexData(data) {
let current = this.head;
let prev = null;
if (this.head === null) {
return null;
}
else if (current.data === data) {
if(!prev) {
this.head = this.head.next;
}
else
prev.next = current.next
}
return this.SearchDelete(data)
}
SearchDelete (data) {
let current = this.head;
let prev = null;
while(current != null) {
if (current.data === data) {
if (!current.next) prev.next = null
else prev.next = current.next
this.size--;
return data;
}
prev = current;
current = current.next;
}
return null;
}
DeleteLastNode() {
let current = this.head;
if (current === null) {
return 1
}
else if (current.next === null) {
this.head = null;
}
else return this.LastNode()
};
LastNode() {
let current = this.head;
while (current.next.next != null) {
current = current.next;
}
current.next = null;
this.size--;
}
Search(data) {
let current = this.head;
if (current === null) {
return null;
}
else
return this.RainbowSix(data)
}
RainbowSix(data) {
let current = this.head;
while (current) {
if (current.data === data) {
return current;
}
current = current.next;
}
return null;
}
Size(){
return this.size
}
}
let list = new ListRecurse();
list.add(1).add(2).add(3).add(44).add(66);
list.insertAdd(33,0)
list.DeleteLastNode()
console.log(list.Search(3))
console.log(list.Size())
console.log(list.Print())
console.log(list);

This may or may not help. It suggests a substantially different way to build your lists.
The idea is that recursion, although occasionally used with Object-Oriented (OO) systems, is much more closely tied to Functional Programming (FP). So if you're going to use recursion on your lists, you might as well use it with FP lists.
Creating and manipulating lists is one of the strengths of FP, and we can write your code much more simply. We create a bare list of one item, 42 by calling const list1 = ins (42) (null). We prepend that with 17 by calling const list2 = ins (17) (list1). Or we can write a whole chain of these like this:
const list3 = ins (1) (ins (2) (ins (3) (ins (4) (ins (5) (null)))))
There are many differences from your code, but one of the most fundamental, is that this treats lists as immutable objects. None of our code will change a list, it will just create a new one with the altered properties.
This is what ins might look like:
const ins = (data) => (list) =>
({data, next: list})
We could choose to write this as (data, list) => ... instead of (data) => (list) => .... That's just a matter of personal preference about style.
But the basic construction is that a list is
a value
followed by either
another list
or null
Here is an implementation of these ideas:
const ins = (data) => (list) =>
({data, next: list})
const del = (target) => ({data, next}) =>
target == data ? next : next == null ? {data, next} : {data, next: del (target) (next)}
const delLast = ({data, next}) =>
next == null ? null : {data, next: delLast (next)}
const size = (list) =>
list == null ? 0 : 1 + size (list.next)
const search = (pred) => ({data, next}) =>
pred (data) ? {data, next} : next != null ? search (pred) (next) : null
const fnd = (target) =>
search ((data) => data == target)
const print = ({data, next}) =>
data + (next == null ? '' : ('=>' + print (next)))
const list1 = ins (1) (ins (2) (ins (3) (ins (44) (ins (66) (null)))))
const list2 = ins (33) (list1)
const list3 = delLast (list2)
console .log (fnd (3) (list3))
console .log (size (list3))
console .log (print (list3))
console .log (list3)
.as-console-wrapper {max-height: 100% !important; top: 0}
Note that all of these functions, except for ins and find are directly recursive. They all call themselves. And find simply delegates the recursive work to search.
It's too much to try to describe all of these functions, but lets look at two. print is a simple function.
const print = ({data, next}) =>
data + (next == null ? '' : ('=>' + print (next)))
We build our output string by including our data followed by one of two things:
an empty string, if next is null
'=>' plus the recursive print call on next, otherwise.
del is a somewhat more complex function:
const del = (target) => ({data, next}) =>
target == data
? next
: next == null
? {data, next: null}
: {data, next: del (target) (next)}
We test if our current data is the target we want to delete. If it is, we simply return the list stored as next.
If not, we check whether next is null. If it is, we return (a copy of) the current list. If it is not, then we return a new list formed by our current data and a recursive call to delete the target from the list stored as next.
If you want to learn more about these ideas, you probably want to search for "Cons lists" ("con" here is not the opposite of "pro", but has to do with "construct"ing something.)
I used different terms than are most commonly used there, but the ideas are much the same. If you run across the terms car and cdr, they are equivalent to our data and next, respectively.

I was working on this answer as Scott made his post, making most of this information redundant. There is a portion which shows how to couple OOP-style with functional (persistent) data structures which you should find helpful.
Similar to Scott's answer, we start by writing plain functions, no classes or methods. I'm going to place mine in a module named list.js -
// list.js
import { raise } from "./func"
const nil =
Symbol("nil")
const isNil = t =>
t === nil
const node = (value, next) =>
({ node, value, next })
const singleton = v =>
node(v, nil)
const fromArray = a =>
a.reduceRight((r, _) => node(_, r), nil)
const insert = (t, v, i = 0) =>
isNil(t)
? singleton(v)
: i > 0
? node(t.value, insert(t.next, v, i - 1))
: node(v, t)
const last = t =>
isNil(t)
? raise("cannot get last element of empty list")
: isNil(t.next)
? t.value
: last(t.next)
const search = (t, q) =>
isNil(t)
? undefined
: t.value === q
? t
: search(t.next, q)
const size = t =>
isNil(t)
? 0
: 1 + size(t.next)
const toString = t =>
isNil(t)
? "Nil"
: `${t.value}->${toString(t.next)}`
const toArray = t =>
isNil(t)
? []
: [ t.value, ...toArray(t.next) ]
Now we can implement our OOP-style, List interface. This gives you the chaining behaviour you want. Notice how the methods are simple wrappers around the plain functions we wrote earlier -
// list.js (continued)
class List
{ constructor(t = nil)
{ this.t = t }
isNil()
{ return isNil(this.t) }
size()
{ return size(this.t) }
add(v)
{ return new List(node(v, this.t)) }
insert(v, i)
{ return new List(insert(this.t, v, i)) }
toString()
{ return toString(this.t) }
}
Finally, make sure to export the parts of your module
// list.js (continued)
export { nil, isNil, node, singleton, fromArray, insert, last, search, size, toArray, toString }
export default List
The List interface allows you to do things in the familiar OOP ways -
import List from "../list"
const t = (new List).add(3).add(2).add(1)
console.log(t.toString())
// 1->2->3->Nil
console.log(t.insert(9, 0).toString())
// 9->1->2->3->Nil
console.log(t.isNil())
// false
console.log(t.size())
// 3
Or you can import your module and work in a more functional way -
import * as list from "../list"
const t = list.fromArray([1, 2, 3])
console.log(list.toString(t))
// 1->2->3->Nil
console.log(list.isNil(t))
// true
console.log(list.size(t))
// 3
I think the important lesson here is that the module functions can be defined once, and then the OOP interface can be added afterwards.
A series of tests ensures the information in this answer is correct. We start writing the plain function tests -
// list_test.js
import List, * as list from "../list.js"
import * as assert from '../assert.js'
import { test, symbols } from '../test.js'
await test("list.isNil", _ => {
assert.pass(list.isNil(list.nil))
assert.fail(list.isNil(list.singleton(1)))
})
await test("list.singleton", _ => {
const [a] = symbols()
const e = list.node(a, list.nil)
assert.equal(e, list.singleton(a))
})
await test("list.fromArray", _ => {
const [a, b, c] = symbols()
const e = list.node(a, list.node(b, list.node(c, list.nil)))
const t = [a, b, c]
assert.equal(e, list.fromArray(t))
})
await test("list.insert", _ => {
const [a, b, c, z] = symbols()
const t = list.fromArray([a, b, c])
assert.equal(list.fromArray([z,a,b,c]), list.insert(t, z, 0))
assert.equal(list.fromArray([a,z,b,c]), list.insert(t, z, 1))
assert.equal(list.fromArray([a,b,z,c]), list.insert(t, z, 2))
assert.equal(list.fromArray([a,b,c,z]), list.insert(t, z, 3))
assert.equal(list.fromArray([a,b,c,z]), list.insert(t, z, 99))
assert.equal(list.fromArray([z,a,b,c]), list.insert(t, z, -99))
})
await test("list.toString", _ => {
const e = "1->2->3->Nil"
const t = list.fromArray([1,2,3])
assert.equal(e, list.toString(t))
assert.equal("Nil", list.toString(list.nil))
})
await test("list.size", _ => {
const [a, b, c] = symbols()
assert.equal(0, list.size(list.nil))
assert.equal(1, list.size(list.singleton(a)))
assert.equal(2, list.size(list.fromArray([a,b])))
assert.equal(3, list.size(list.fromArray([a,b,c])))
})
await test("list.last", _ => {
const [a, b, c] = symbols()
const t = list.fromArray([a,b,c])
assert.equal(c, list.last(t))
assert.throws(Error, _ => list.last(list.nil))
})
await test("list.search", _ => {
const [a, b, c, z] = symbols()
const t = list.fromArray([a, b, c])
assert.equal(t, list.search(t, a))
assert.equal(list.fromArray([b, c]), list.search(t, b))
assert.equal(list.singleton(c), list.search(t, c))
assert.equal(undefined, list.search(t, z))
})
await test("list.toArray", _ => {
const [a,b,c] = symbols()
const e = [a,b,c]
const t = list.fromArray(e)
assert.equal(e, list.toArray(t))
})
Next we ensure the List interface behaves accordingly -
// list_test.js (continued)
await test("List.isNil", _ => {
assert.pass((new List).isNil())
assert.fail((new List).add(1).isNil())
})
await test("List.size", _ => {
const [a,b,c] = symbols()
const t1 = new List
const t2 = t1.add(a)
const t3 = t2.add(b)
const t4 = t3.add(c)
assert.equal(0, t1.size())
assert.equal(1, t2.size())
assert.equal(2, t3.size())
assert.equal(3, t4.size())
})
await test("List.toString", _ => {
const t1 = new List
const t2 = (new List).add(3).add(2).add(1)
assert.equal("Nil", t1.toString())
assert.equal("1->2->3->Nil", t2.toString())
})
await test("List.insert", _ => {
const t = (new List).add(3).add(2).add(1)
assert.equal("9->1->2->3->Nil", t.insert(9, 0).toString())
assert.equal("1->9->2->3->Nil", t.insert(9, 1).toString())
assert.equal("1->2->9->3->Nil", t.insert(9, 2).toString())
assert.equal("1->2->3->9->Nil", t.insert(9, 3).toString())
assert.equal("1->2->3->9->Nil", t.insert(9, 99).toString())
assert.equal("9->1->2->3->Nil", t.insert(9, -99).toString())
})
Dependencies used in this post -
func.raise - allows you to raise an error using an expression instead of a throw statement
// func.js
const raise = (msg = "", E = Error) => // functional throw
{ throw E(msg) }
// ...
export { ..., raise }

ANDing on array of function

Given:
const a = () => true
const b = () => false
const t = [a, b]
How can I generate an additive AND:
a() && b()
In this case, it would return false.

You could reduce the array by using true as startValue and perform a logical AND && by using the result of the function call.
This approach keeps the value of the function calls.
const a = () => true
const b = () => false
const t = [a, b]
console.log(t.reduce((r, f) => r && f(), true));
Approach with a stored value for the result and a short circuit.
const AND = array => {
var result = true;
array.every(fn => result = result && fn());
return result;
};

Use array.every():
const a = () => true
const b = () => false
const t = [a, b]
console.log(t.every(f => f()));
This will only produce a boolean value, so if you were intending to get a different result as if short circuiting you'll have to use a reduce() solution or other.

In your case, using a() && b() will work perfectly. If you want to use the t array, you can do it like this: t[0]() && t[1](). However, if you want multiple inputs, I think it would be good to use an array function (Array.prototype.reduce):
t.reduce((previous, item) => previous && item(), true)

Use Array.find() to get the 1st function with a falsy value. If none found, take the last function in the array, and if the array is empty use the fallback function that returns undefined. Invoke the function that you got.
const fn = arr => (
arr.find(f => !f()) || arr[arr.length - 1] || (() => undefined)
)()
console.log(fn([() => true, () => false])) // false
console.log(fn([() => 1, () => 2])) // 2
console.log(fn([() => 1, () => 0, () => 2])) // 0
console.log(fn([])) // undefined

JavaScript call multi function, but input value is output from last function

I have a function like that:
function intiFun(initValue) {
const firstResult = firstFun(initValue);
const secondResult = secondFun(firstResult);
const thirdResult = thirddFun(secondResult);
const fourthResult = fourthFun(thirdResult);
return fourthResult;
}
but i want to write it better. and i dont want to save value from each function as variable.
is there any solution to to call functions with out save old value
like rxjs or somthing like that:
function intiFun(initValue) {
return firstFun(initValue).secondFun().thirddFun().fourthFun();
}
or more better like that:
function intiFun(initValue) {
return firstFun(initValue)
.secondFun(secondInput)
.thirddFun(secondInput)
.fourthFun(secondInput)
}
function secondFun(value, secondInput) {
return ...;
}
...
or some liberally to do that (maybe lodash)

My guess is you're looking for function composition: we can construct the composite function from an array of functions in JavaScript using for example reduce (with the initial value being the identity function (v) => v:
const composeAll = (functions) => functions.reduce(
(composition, f) =>
((v) => f(composition(v))),
(v) => v
);
const firstFun = (s) => `${s}a`;
const secondFun = (s) => `${s}b`;
const thirdFun = (s) => `${s}c`;
const fourthFun = (s) => `${s}d`;
const intiFun = composeAll([firstFun, secondFun, thirdFun, fourthFun]);
console.log(intiFun(''));
OUTPUT:
abcd
NOTES:
As you can see, composeAll creates a chained function call by wrapping each function f in an arrow function which takes a value v, executes it on the composite function constructed from the preceding functions in the array and finally passes the result to f.
You can convince yourself that the construction is correct by induction over the array length: if we define the composition of an empty list of functions to be the identity function then
in the base case (for a singleton array [f] with length 1) the result is
(v) => f((v => v)(v)) === (v) => f(v)
in the step case (for an array with length n) assume the function obtained for the n-1 preceding functions in the array was correctly constructed (let this be g), then the result is
(v) => f_n(g(v)) === (v) => f_n(f_n-1(...(f_0(v))...))

pipe, manual currying & partial application to the rescue:
const pipe = funs => x =>
funs.reduce ((o, fun) => fun (o), x)
const f = x => x + 1
const g = x => y => x + y * 2
const h = x => x * x
const i = x => y => z => x + y / z + 3
const j = x => x + 5
const init = pipe ([
f
,g (4)
,h
,i (10) (33)
,j
])
const input = 1
const output = init (input)
console.log (output)

You can do something like this
const firstFun = x => x + 1;
const secondFun = x => x + 1;
const thirdFun = x => x + 1;
const fourthFun = x => x + 1;
const pipe = (...functions) => x => functions.reduce((x, f) => f(x), x);
const initFun = pipe(firstFun, secondFun, thirdFun, fourthFun);
console.log(initFun(3));

const firstFun = x => { /* return ... */ };
const secondFun = x => { /* return ... */ };
const thirdFun = x => { /* return ... */ };
const fourthFun = x => { /* return ... */ };
const callAll= (value, ...functions) => {
functions.forEach(fn => value = fn(value));
retrun value;
}
const result = callAll(3, firstFun, secondFun, thirdFun, fourthFun);
console.log(result);

The result you're looking for can be achieved using reduce.
let log = (head, ...args) => { console.log('log:', head, ...args); return head },
firstFun = (str, ...args) => log(str, ...args) + ' firstFun',
secondFun = (str, ...args) => log(str, ...args) + ' secondFun',
thirddFun = (str, ...args) => log(str, ...args) + ' thirddFun',
fourthFun = (str, ...args) => log(str, ...args) + ' fourthFun';
function initFun(initValue) {
let functions = [
[firstFun],
[secondFun, 'extra argument'],
[thirddFun],
[fourthFun, "I'm here too"],
];
return functions.reduce((result, [fn, ...args]) => fn(result, ...args), initValue);
}
console.log( 'result: ' + initFun('foo bar') );
Keep in mind that I log the incomming arguments of the methods, not the resulting value. This means that for example secondFun (log: foo bar firstFun extra argument) has the argument 'foo bar firstFun' and 'extra argument'. But you only see the added string 'secondFun' when thirdFun is called (since it is given as the argument).

function initFun(initValue) {
return fourthFun(thirddFun(secondFun(firstFun(initValue))));
}
Alternatively, convert your function into promises:
function initFun(initValue) {
return firstFun(initValue)
.then(secondFun)
.then(thirddFun)
.then(fourthFun);
}

Bad Method — See Below
If you want something like a.firstFunc().secondFunc().thirdFunc().fourthFunc(), you should define those functions to Object.prototype (or Number.prototype, String.prototype, etc.):
Object.prototype.firstFunc = function() {
var value = this;
// ...
return something;
};
Object.prototype.secondFunc = function() {
var value = this;
// ...
return something;
};
Object.prototype.thirdFunc = function() {
var value = this;
// ...
return something;
};
Object.prototype.fourthFunc = function() {
var value = this;
// ...
return something;
};
P.S. "Function" is normally shortened to "func" but not "fun".
Update
If you want something like myObject(a).firstFunc().secondFunc().thirdFunc().fourthFunc(), you should:
var myObject = function(value) {
this.value = value;
};
myObject.prototype.firstFunc = function() {
var value = this.value;
// ...
return something;
};
myObject.prototype.secondFunc = function() {
var value = this.value;
// ...
return something;
};
myObject.prototype.thirdFunc = function() {
var value = this.value;
// ...
return something;
};
myObject.prototype.fourthFunc = function() {
var value = this.value;
// ...
return something;
};

How to correctly serialize Javascript curried arrow functions?

const makeIncrementer = s=>a=>a+s
makeIncrementer(10).toString() // Prints 'a=>a+s'
which would make it impossible to de-serialize correctly (I would expect something like a=>a+10 instead.
Is there a way to do it right?

This is a great question. While I don't have a perfect answer, one way you could get details about the argument/s is to create a builder function that stores the necessary details for you. Unfortunately I can't figure out a way to know which internal variables relate to which values. If I figure out anything else i'll update:
const makeIncrementer = s => a => a + s
const builder = (fn, ...args) => {
return {
args,
curry: fn(...args)
}
}
var inc = builder(makeIncrementer, 10)
console.log(inc) // logs args and function details
console.log(inc.curry(5)) // 15
UPDATE: It will be a mammoth task, but I realised, that if you expand on the builder idea above, you could write/use a function string parser, that could take the given args, and the outer function, and rewrite the log to a serialised version. I have a demo below, but it will not work in real use cases!. I have done a simple string find/replace, while you will need to use an actual function parser to replace correctly. This is just an example of how you could do it. Note that I also used two incrementer variables just to show how to do multiples.
function replaceAll(str, find, replace) {
return str.replace(new RegExp(find, 'g'), replace)
}
const makeIncrementer = (a, b) => c => c + a + b
const builder = (fn, ...args) => {
// get the outer function argument list
var outers = fn.toString().split('=>')[0]
// remove potential brackets and spaces
outers = outers.replace(/\(|\)/g,'').split(',').map(i => i.trim())
// relate the args to the values
var relations = outers.map((name, i) => ({ name, value: args[i] }))
// create the curry
var curry = fn(...args)
// attempt to replace the string rep variables with their true values
// NOTE: **this is a simplistic example and will break easily**
var serialised = curry.toString()
relations.forEach(r => serialised = replaceAll(serialised, r.name, r.value))
return {
relations,
serialised,
curry: fn(...args)
}
}
var inc = builder(makeIncrementer, 10, 5)
console.log(inc) // shows args, serialised function, and curry
console.log(inc.curry(4)) // 19

You shouldn't serialize/parse function bodies since this quickly leads to security vulnerabilities. Serializing a closure means to serialize its local state, that is you have to make the closure's free variables visible for the surrounding scope:
const RetrieveArgs = Symbol();
const metaApply = f => x => {
const r = f(x);
if (typeof r === "function") {
if (f[RetrieveArgs])
r[RetrieveArgs] = Object.assign({}, f[RetrieveArgs], {x});
else r[RetrieveArgs] = {x};
}
return r;
}
const add = m => n => m + n,
f = metaApply(add) (10);
console.log(
JSON.stringify(f[RetrieveArgs]) // {"x":10}
);
const map = f => xs => xs.map(f)
g = metaApply(map) (n => n + 1);
console.log(
JSON.stringify(g[RetrieveArgs]) // doesn't work with higher order functions
);
I use a Symbol in order that the new property doesn't interfere with other parts of your program.
As mentioned in the code you still cannot serialize higher order functions.

Combining ideas from the two answers so far, I managed to produce something that works (though I haven't tested it thoroughly):
const removeParentheses = s => {
let match = /^\((.*)\)$/.exec(s.trim());
return match ? match[1] : s;
}
function serializable(fn, boundArgs = {}) {
if (typeof fn !== 'function') return fn;
if (fn.toJSON !== undefined) return fn;
const definition = fn.toString();
const argNames = removeParentheses(definition.split('=>', 1)[0]).split(',').map(s => s.trim());
let wrapper = (...args) => {
const r = fn(...args);
if (typeof r === "function") {
let boundArgsFor_r = Object.assign({}, boundArgs);
argNames.forEach((name, i) => {
boundArgsFor_r[name] = serializable(args[i]);
});
return serializable(r, boundArgsFor_r);
}
return r;
}
wrapper.toJSON = function () {
return { function: { body: definition, bound: boundArgs } };
}
return wrapper;
}
const add = m => m1 => n => m + n * m1,
fn = serializable(add)(10)(20);
let ser1, ser2;
console.log(
ser1 = JSON.stringify(fn) // {"function":{"body":"n => m + n * m1","bound":{"m":10,"m1":20}}}
);
const map = fn => xs => xs.map(fn),
g = serializable(map)(n => n + 1);
console.log(
ser2 = JSON.stringify(g) // {"function":{"body":"xs => xs.map(fn)","bound":{"fn":{"function":{"body":"n => n + 1","bound":{}}}}}}
);
const reviver = (key, value) => {
if (typeof value === 'object' && 'function' in value) {
const f = value.function;
return eval(`({${Object.keys(f.bound).join(',')}}) => (${f.body})`)(f.bound);
}
return value;
}
const rev1 = JSON.parse(ser1, reviver);
console.log(rev1(5)); // 110
const rev2 = JSON.parse(ser2, reviver);
console.log(rev2([1, 2, 3])); // [2, 3, 4]
This works for arrow functions, that do not have default initializers for the arguments. It supports higher order functions as well.
One still has to be able to wrap the original function into serializable before applying it to any arguments though.
Thank you #MattWay and #ftor for valuable input !

How to get a functions's body as string?

I want to know how to convert a function's body into a string?
function A(){
alert(1);
}
output = eval(A).toString() // this will come with function A(){ ~ }
//output of output -> function A(){ alert(1); }
//How can I make output into alert(1); only???

If you're going to do something ugly, do it with regex:
A.toString().match(/function[^{]+\{([\s\S]*)\}$/)[1];

Don't use a regexp.
const getBody = (string) => string.substring(
string.indexOf("{") + 1,
string.lastIndexOf("}")
)
const f = () => { return 'yo' }
const g = function (some, params) { return 'hi' }
const h = () => "boom"
console.log(getBody(f.toString()))
console.log(getBody(g.toString()))
console.log(getBody(h.toString())) // fail !

You could just stringify the function and extract the body by removing everything else:
A.toString().replace(/^function\s*\S+\s*\([^)]*\)\s*\{|\}$/g, "");
However, there is no good reason to do that and toString actually doesn't work in all environments.

Currently, developers are using arrow functions with the new releases of Ecmascript.
Hence, I would like to share the answer here which is the answer of Frank
function getArrowFunctionBody(f) {
const matches = f.toString().match(/^(?:\s*\(?(?:\s*\w*\s*,?\s*)*\)?\s*?=>\s*){?([\s\S]*)}?$/);
if (!matches) {
return null;
}
const firstPass = matches[1];
// Needed because the RegExp doesn't handle the last '}'.
const secondPass =
(firstPass.match(/{/g) || []).length === (firstPass.match(/}/g) || []).length - 1 ?
firstPass.slice(0, firstPass.lastIndexOf('}')) :
firstPass
return secondPass;
}
const K = (x) => (y) => x;
const I = (x) => (x);
const V = (x) => (y) => (z) => z(x)(y);
const f = (a, b) => {
const c = a + b;
return c;
};
const empty = () => { return undefined; };
console.log(getArrowFunctionBody(K));
console.log(getArrowFunctionBody(I));
console.log(getArrowFunctionBody(V));
console.log(getArrowFunctionBody(f));
console.log(getArrowFunctionBody(empty));
Original question here

This coud be what youre looking for
const toString = (func) => `(${func.toString()})()`
console.log(toString(() => {
console.log("Hello world")
}))
This will execute the function.

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