A function that counts how often it calls another function
I have a function "twice" that returns 2 arguments passed into it. I also have another function "runTwice" that counts the number of times it has called the function "twice" (the idea is that I only want the function "twice" to execute "twice", no matter how often it is called via "runTwice" '). Could you help me?
The functions are listed below:
var count = 1;
function twice(num){
return num*2;
}
function runTwice(func){
if (count<3){
count++;
return func;
} else {
return 'Function cannot run!';
}
}
var myFunc = runTwice(twice)
var output = [];
for (var i = 0; i < 3; i++){
output.push(myFunc(i));
}
console.log(output);
I would like the output to be [0, 2, "Function cannot work!" ].
I can make this work if I count the function "twice", but I want to understand why it doesn't work as shown above.
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The function runTwice
should return another function that decides whether the function should be called func
(using ) or to return a string message: Function.prototype.apply
function twice(num){
return num * 2;
}
function runTwice(func){
var count = 0; // this will be trapped in a closure along with func
return function() { // this is the function that gets called
count++; // it increments its version of the count variable
if(count <= 2) // if count is less than 2
return func.apply(this, arguments); // then it calls the function func with whatever arguments passed into it and return the returned value of that call
return "Not available anymore!"; // otherwise (count > 2), then it returns a string
}
}
var myFunc = runTwice(twice);
for (var i = 0; i < 3; i++){
console.log(myFunc(i));
}
Better:
You can also specify the number of times allowed:
function double(num) {
return num * 2;
}
function triple(num) {
return num * 3;
}
function run(func, times){
var count = 0; // this will be trapped in a closure along with func and times
return function() { // this is the function that gets called
count++; // it increments its version of the count variable
if(count <= times) // if count is less than times
return func.apply(this, arguments); // then it calls the function func with whatever arguments passed into it and return the returned value of that call
return "Not available anymore!"; // otherwise (count > times), then it returns a string
}
}
var double2times = run(double, 2); // double2times can only be called 2 times
var triple5times = run(triple, 5); // triple5times can only be called 5 times
for (var i = 0; i < 10; i++){
console.log("Double:", double2times(i));
console.log("Triple:", triple5times(i));
}
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Just for fun, I'll create a generic function expireAfter(invocable[, times[, message]])
:
function expireAfter(invocable, times = 2, message = 'Function cannot run!') {
return function expires() {
if (times > 0) {
times--;
return invocable.apply(this, arguments);
}
return message;
}
}
function twice(n) {
return n * 2;
}
var myFunc = expireAfter(twice);
console.log(Array(3)
.fill()
.map((_, index) => myFunc(index))
);
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