creating a spy function using javascript - javascript

I am trying to build a spy function that will do this.
const func1 = function (x, y) {return x + y};
const func2 = spy(func1);
func2(2, 5) // => 7
func2(4, 5) // => 9
func2.calls() // => 2
func2.args() // => [[2, 5], [4, 5]]
I have created this function but I can seem to get the calls and args
function spy(func) {
let count = 0;
let allArgs = [];
function ispy() {
let args2 = Array.prototype.slice.call(arguments);
spy.calls = function() {
return count++;
}
spy.args = function() {
return allArgs.push(args2)
}
func.apply(this, args2);
}
return spy;
}
const func1 = function (x, y) {return x + y};
const func2 = spy(func1);
console.log(func2(2, 5))
console.log(func2.calls())
console.log(func2.args())
Please help me fix it and let me know what am I missing?

A few things,
You need to keep track of count and allArgs for every invocation of the spy call.
You need to return the result of the spied upon function from spy.
function spy(func) {
let count = 0;
let allArgs = [];
function spy() {
// increment count on every invocation
count++;
let args2 = Array.prototype.slice.call(arguments);
// shove arguments onto the allArgs array.
allArgs.push(args2);
spy.calls = function() {
return count;
}
spy.args = function() {
return allArgs;
}
//return the result;
return func.apply(this, args2);
}
return spy;
}
const func1 = function (x, y) {return x + y};
const func2 = spy(func1);
console.log(func2(2, 5))
console.log(func2.calls())
console.log(func2.args())

You add functions to spy in a call of ispy() and increment count in call of calls instead of call of ispy, you don't return result of func, you assign calls and args functions in every call to ispy and many other mistakes
function spy(func) {
let count = 0;
let allArgs = [];
function ispy(...args) {
count++;
allArgs.push(args);
return func.apply(this, args);
}
ispy.calls = function() {
return count;
}
ispy.args = function() {
return allArgs;
}
return ispy;
}
const func1 = function (x, y) {return x + y};
const func2 = spy(func1);
console.log(func2(2, 5));
console.log(func2(4, 5));
console.log(func2.calls())
console.log(func2.args())

You could take the arguments directly with rest parameters and return in the function only the value of the variables. The assignemnt should happen outside of the function, because if not it would require a call of func2 first.
Each call of ispy should be counted and the arguments should be added to.
function spy(func) {
function ispy(...args) {
count++;
allArgs.push(args);
return func.apply(this, args);
}
let count = 0;
let allArgs = [];
ispy.calls = () => count;
ispy.args = () => allArgs;
return ispy;
}
const func1 = function (x, y) {return x + y};
const func2 = spy(func1);
console.log(func2.calls())
console.log(func2(2, 5))
console.log(func2.calls())
console.log(func2.args())

Related

Implement redux compose function but get RangeError

I am trying to re-implement redux compose function, instead of using reduce i use a for loop, here is my code:
function compose(...funcs) {
if (funcs.length === 0) {
return (arg) => arg;
}
if (funcs.length === 1) {
return funcs[0];
}
let result;
for (let i = funcs.length - 1; i > -1; i--) {
result = result
? (...args) => funcs[i](result(...args))
: (...args) => funcs[i](...args);
}
return result;
}
// test
function fn1(x) {
return x + 1;
}
function fn2(x) {
return x * 10;
}
function fn3(x) {
return x - 1;
}
console.log(compose(fn3, fn2, fn1)(10)); // 109
It is expected to log 109 since (10 + 1) * 10 - 1 is 109, however it gives me such error:
RangeError: Maximum call stack size
Looks like i am doing some recursion but all i did is just a for loop, no sure where is the problem of my code?
I think the issue is like the below example:
a = () => 2;
a = () => 3 * a();
console.log(a);
// this prints () => 3 * a() in console
// so when you call a(), it will call 3 * a(), which will again call 3 * a() and so on
// leading to infinite recursion
My solution is slightly different using bind function based on this reference link: https://stackoverflow.com/a/6772648/4688321.
I think bind creates a new copy of the function result and binds it to a new object. Not using bind leads to recursion because then the code becomes like the above example, result calls result.
function compose(...funcs) {
if (funcs.length === 0) {
return (arg) => arg;
}
if (funcs.length === 1) {
return funcs[0];
}
let result;
for (let i = funcs.length - 1; i > -1; i--) {
if (i == funcs.length - 1)
result = (...args) => funcs[i](...args);
else {
let temp = result.bind({});
result = (...args) => funcs[i](temp(...args));
}
}
return result;
}
// test
function fn1(x) {
console.log("fn1");
return x + 1;
}
function fn2(x) {
console.log("fn2");
return x * 10;
}
function fn3(x) {
console.log("fn3");
return x - 1;
}
//console.log(compose(fn3, fn2, fn1));
let ret = compose(fn3, fn2, fn1);
console.log(ret(10)); // 109
Rather than trying to combine functions at the time of compose, it seems much easier to combine them at the time the resulting function is called:
function compose(...funcs) {
if (funcs.length === 0) {
return (arg) => arg
}
return function (...args) {
let result = funcs .at (-1) (...args)
for (let i = funcs.length - 2; i > -1; i--) {
result = funcs [i] (result)
}
return result
}
}
// test
function fn1(x) {
return x + 1;
}
function fn2(x) {
return x * 10;
}
function fn3(x) {
return x - 1;
}
console.log(compose(fn3, fn2, fn1)(10)); // 109
However, again, reduce make for a much cleaner implementation:
const compose = (...fns) => (arg) =>
fns .reduceRight ((a, fn) => fn (a), arg)
or if you want to allow the rightmost function to receive multiple variables, then
const compose = (...fns) => (...args) =>
fns .reduceRight ((a, fn) => [fn (...a)], args) [0]

Calling a Javascript Function as a Primitive Datatype(Number in particular)

I am trying out some new implementations for a project in express and i have this issue:
code snippet:
let add_1 = () =>{
console.log(2)
}
let a = add_1();
let add_2 = () => {
console.log(5)
}
let z = add_2();
console.log(a +z);
upon running this code snippet i get a NaN
is there a way i can return the actual addition of these function calls (which in this case is 2+5=7) ?
you should use return statement instead of console.log like below
let add_1 = () =>{
return 2;
}
let a = add_1();
let add_2 = () => {
return 5;
}
let z = add_2();
console.log(a +z);
Your functions print to console but they do not return a value, so you cannot add them as numbers.
You can have each function do this return 5; or return 2; after the console.log(..) statement.
You can also user variables (instead of hard-coded values) or pass in parameters to the functions.
See below:
let add_1 = () => {
const val = 2;
console.log(val);
return val;
}
let a = add_1();
let add_2 = (val) => {
console.log(val);
return val;
}
let z = add_2(5);
console.log(a + z);
console.log(a + a);
console.log(z + z);

Execute Multiple functions in a function

function executeActions(param)
{
if((param != undefined) && (param.length > 0))
{
for(i=0; i < param.length; i++)
{
//eval like function
param[i]();
}
}
}
function clearFields()
{
...
}
function showAbs(param)
{
if(param == 'insert')
{
...
}
else if(param == 'update')
{
...
}
else
{
...
}
}
$("#clearButton").click(function(event)
{
//var functions = ["clearFields()","showAbs('insert')"];
var a = showAbs('insert');
var functions = [clearFields, a];
executeActions(functions);
});
Hello everyone!
How can I execute some functions with parameters in a row in a set of instructions like i've showed above?
If they don't have any parameters, then the functions execute like in chain, but, if one or more of them uses
some parameters, it stops with the error: "param[i] is not a function".
Maybe if you have another elegant solution for this code, i'd appreciate if you share with us.
Thank you all in advance!
You can use partial application for this. Partial application means that you take a given function and fix one or more parameters to it. Example
function sum(a, b){
return a + b;
}
function product(a, b){
return a * b;
}
function doSomething(){
// do something
}
function runFunctions(funcs){
for(var i = 0;i<funcs.length;i++){
funcs[i]();
}
}
var mySum = function(){
return sum(5, 6);
}
var myProduct = function(){
return product(2, 3);
}
runFunctions(mySum, myProduct, doSomething);
The above is using ES 5 syntax. You could make this a bit more concise using ES 6 syntax:
const sum = (a, b) => a + b;
const product = (a, b) => a * b;
const doSomething = () => // do something
const runFunctions = funcs => {
for(func of funcs)
func();
}
var mySum = () => sum(5, 6);
var myProduct = () => product(2, 3);
runFunctions(mySum, myProduct, doSomething);
or you could use the bind function to take care of fixing the vars:
const sum = (a, b) => a + b;
const product = (a, b) => a * b;
const doSomething = () => // do something
const runFunctions = funcs => {
for(func of funcs)
func();
}
runFunctions(sum.bind(null, 5,6), myProduct.bind(null, 2,3), doSomething);
For me a way you want to achieve may be not readable for other developers.
You may create a function that will group all your function executions like:
function groupedFunctions{
return {
A: funcA(param),
B: funcB(param),
C: funcC(param)
}
}
function executeActions(funcObj, params) {
funcObj.A(params.a);
funcObj.B(params.b);
}
let params = {a: 1, b:2}
executeActions(groupedFunction(), params)

Javascript: making functions at runtime

update
solution works in foreach loop but not in for loop
function x(number){
return number - 10;
}
var i = 0
var runtimefunctions = {};
var allLevels = {"1":"State","2":"Educational_Services","3":"Principal_Networks","4":"Schools"}
for (var key in allLevels) {
runtimefunctions[i] = function() { return x(i); };
i++;
};
console.log(runtimefunctions[1]()); // -6
console.log(runtimefunctions[2]()); // -6
console.log(runtimefunctions[3]()); // -6
tried hard to make functions but it's first time to create such thing so cant understand the proper way...
I have a function..
function x(number){
return number - 10;
}
runtimefunctions = {};
now I have a loop to run
[1,2,3].forEach(function(y){
//here I want to create a function.. which will make a function x(y) -- like this
runtimefunctions[x] = new Function("return function x_" + levelIterator + "(levelIterator){ console.log(levelIterator); x(" + y + ") }")();
});
so basically..want to make functions like this.
runtimefunctions= {
"1": x(1),
"2": x(2),
and so on
}
Is this what you need?
function x(number){
return number - 10;
}
var runtimefunctions = {};
[1,2,3].forEach(function(y){
runtimefunctions[y] = function() { return x(y); };
});
console.log(runtimefunctions[1]()); // -9
console.log(runtimefunctions[2]()); // -8
console.log(runtimefunctions[3]()); // -7
To satisfy your next (for-in) requirement, you need to closure the index variable with additional function call:
var runtimefunctions = {}, i = 0;
var allLevels = {"1":"State","2":"Educational_Services","3":"Principal_Networks","4":"Schools"}
for (var key in allLevels) {
runtimefunctions[i] = function(index){ return function() { return x(index); } }(i++);
};
It is much easier.
For example:
const createFunctionWith = (x) => {
return (param) => console.log(x, param)
}
let a = [1,2,3].map(x => createFunctionWith(x));
console.log(a[1]("bebe")); // 2, "bebe"
https://jsfiddle.net/muLxoxLd/
You could do something like this
// Found in your code
var x = (a) => {
console.log(a)
};
var runtimefunctions = {};
[1, 2, 3].forEach(function(y) {
//Create a function with a parameter named "levelIterator"
runtimefunctions[y] = Function("levelIterator", "{ console.log(levelIterator); x(" + y + ") }");
});
runtimefunctions[1]('test')

how to write a sum function with infinite number of arguments, using currying in javascript?

I have tried writing the below code to find sum of 'n' numbers using sum function. I am getting the correct response in output. But i am unable to return that using sum function, as i always have to return a function, which is required for curried effect.
Please help. Thanks in advance.
var output = 0,
chain;
function sum() {
var args = Array.prototype.slice.call(arguments);
output += args.reduce(function(a, b) {
return a + b;
});
sumCurried = sum.bind(output);
sumCurried.val = function() {
return output;
}
return sumCurried;
}
debugger;
document.getElementById('demo').innerHTML = sum(1, 2)(3)(4);
// document.getElementById('demo').innerHTML = sum(1)(3)(4);
<p id='demo'></p>
enter code here
You can add a stop condition to the curried function, for example - if the function is called without an argument return the output:
var output = 0,
chain;
function sum() {
var args = Array.prototype.slice.call(arguments);
if(args.length === 0) {
return output;
}
output += args.reduce(function(a, b) {
return a + b;
});
sumCurried = sum.bind(output);
return sumCurried;
}
console.log(sum(1, 2)(3)(4)());
<p id='demo'></p>
The returned curry function has a val property, which is a function that returns the current value:
var output = 0,
chain;
function sum() {
var args = Array.prototype.slice.call(arguments);
output += args.reduce(function(a, b) {
return a + b;
});
sumCurried = sum.bind(output);
sumCurried.val = function() {
return output;
}
return sumCurried;
}
console.log(sum(1, 2)(3)(4).val());
<p id='demo'></p>
Why would you use currying at all? However, here is a shorter version:
const sum = (...args) => {
const func = (...s)=> sum(...args,...s);
func.value = args.reduce((a,b)=>a+b,0);
return func;
};
//usable as
sum(1,2).value,
sum(1,1)(1).value,
sum(1,1)(1,1)(1,1).value
And you always need to end the currying chain. However, it can be shortified:
func.valueOf = ()=> args.reduce((a,b)=>a+b,0);
//( instead of func.value = ... )
So when called you can do:
+sum(1,2,3)
+sum(1)(1)(1)

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