You can find all the code in this post at repo Github.
Closure related challenges
Hello World
/**
* @return {Function}
*/
function createHelloWorld() {
return function (...args) {
return "Hello World";
};
}
// Usage example
const output = createHelloWorld();
console.log(output()); // => "Hello World"
add
/**
* @param {...any} args
* @return {Function | number}
*/
function add(...args) {
let sum = args.reduce((acc, val) => acc + val, 0);
function innerAdd(...moreArgs) {
sum += moreArgs.reduce((acc, val) => acc + val, 0);
return innerAdd;
}
innerAdd.getValue = function () {
return sum;
};
return innerAdd;
}
// Usage example
console.log(add(1).getValue()); // => 1
console.log(add(1)(2).getValue()); // => 3
console.log(add(1)(2)(3).getValue()); // => 6
console.log(add(1)(2, 3).getValue()); // => 6
console.log(add(1, 2)(3).getValue()); // => 6
console.log(add(1, 2, 3).getValue()); // => 6
Sum
/**
* @param {number} num
*/
function sum(num) {
const func = function (num2) {
return num2 ? sum(num + num2) : num;
};
func.valueOf = () => num;
return func;
}
// Usage example
const sum1 = sum(1);
console.log(sum1(2) == 3); // => true
console.log(sum1(3) == 4); // => true
console.log(sum(1)(2)(3) == 6); // => true
console.log(sum(5)(-1)(2) == 6); // => true
Counter
/**
* @param {number} initialValue
* @return {Function}
*/
function makeCounter(initialValue = 0) {
let count = initialValue - 1;
return function (...args) {
count += 1;
return count;
};
}
// Usage example
const counter = makeCounter(0);
console.log(counter()); // => 0
console.log(counter()); // => 1
console.log(counter()); // => 2
//------------------------------
// return an object
/**
* @param {number} initialValue
* @return {{get: Function, increment: Function, decrement: Function, reset: Function }}
*/
function makeCounter(initialValue = 0) {
let count = initialValue;
return {
get: () => count,
increment: () => ++count,
decrement: () => --count,
reset: () => (count = initialValue),
};
}
// Usage example
const counterObj = makeCounter(0);
console.log(counterObj.get()); // => 0
counterObj.increment();
console.log(counterObj.get()); // => 1
counterObj.decrement();
counterObj.reset();
console.log(counterObj.get()); // => 0
Cycle
/**
* @template T
* @param {...T} values
* @returns () => T
*/
function cycle(...values) {
let index = -1;
return function (...args) {
index = (index + 1) % values.length;
return values[index];
};
}
// Usage example
const helloFn = cycle("hello");
console.log(helloFn()); // => "hello"
console.log(helloFn()); // => "hello"
const onOffFn = cycle("on", "off");
console.log(onOffFn()); // => "on"
console.log(onOffFn()); // => "off"
console.log(onOffFn()); // => "on"
Limit
/**
* @param {Function} func
* @param {Number} count
* @return {Function}
*/
function limit(fn, max) {
let count = 0;
let value;
return function (...args) {
if (count < max) {
value = fn.call(this, ...args);
count++;
}
return value;
};
}
// Usage example
let i = 1;
function incrementBy(value) {
i += value;
return i;
}
const incrementByAtMostThrice = limit(incrementBy, 3);
console.log(incrementByAtMostThrice(2)); // i is now 3; The function returns 3.
console.log(incrementByAtMostThrice(3)); // i is now 6; The function returns 6.
console.log(incrementByAtMostThrice(4)); // i is now 10; The function returns 10.
console.log(incrementByAtMostThrice(5)); // i is still 10 as this is the 4th invocation; The function returns 10 as it's the result of the last invocation.
i = 4;
console.log(incrementByAtMostThrice(2)); // i is still 4 as it is not modified. The function still returns 10.
Once
/**
* @param {Function} fn
* @return {Function}
*/
function once(fn) {
let ranOnce = false;
let value;
return function (...args) {
if (!ranOnce) {
value = fn.call(this, ...args);
ranOnce = true;
}
return value;
};
}
// Usage example
function func(num) {
return num;
}
const onced = once(func);
console.log(onced(1)); // => 1, func called with 1
console.log(onced(2)); // => 1, even 2 is passed, previous result is returned
To be or not to be
/**
* @param {any} val
* @return {true | Error}
*/
function expect(val) {
return {
toBe: function (arg) {
if (val === arg) {
return true;
} else {
throw new Error("Not Equal");
}
},
notToBe: function (arg) {
if (val !== arg) {
return true;
} else {
throw new Error("Equal");
}
},
};
}
// Usage example
expect(5).toBe(5); // Passes
expect(5).notToBe(6); // Passes
try {
expect(5).toBe(6); // Throws an error
} catch (error) {
console.log(error.message); // Not Equal
}
Reference
- 148. create a counter object - BFE.dev
- 2620. Counter - LeetCode
- 2665. Counter II - LeetCode
- 2665. Counter II - LeetCode
- GreatFrontEnd
- 2667. Create Hello World Function - LeetCode
- 23. create a sum() - BFE.dev
- 46. implement
_.once()
- BFE.dev - 2704. To Be Or Not To Be - BFE.dev
- 161. toBe() or not.toBe() - BFE.dev
- "Hello, World!" program - Wikipedia.org
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