add kata

5kyu/a-chain-adding-function/description.md

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+We want to create a function that will add numbers together when called in succession.
+```ts
+add(1)(2); // == 3
+```
+We also want to be able to continue to add numbers to our chain.
+```ts
+add(1)(2)(3); // == 6
+add(1)(2)(3)(4); //  == 10
+add(1)(2)(3)(4)(5); // == 15
+```
+and so on.
+
+A single call should be equal to the number passed in.
+```ts
+add(1); // == 1
+```
+We should be able to store the returned values and reuse them.
+```ts
+var addTwo = add(2);
+addTwo; // == 2
+addTwo + 5; // == 7
+addTwo(3); // == 5
+addTwo(3)(5); // == 10
+```
+We can assume any number being passed in will be valid whole number.

5kyu/a-chain-adding-function/solution.ts

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+
+export default function add(x: number): any {
+  const sum = (y: number): any => add(x + y);
+  // set .valueOf to return the current sum when the object is coerced to a primitive
+  // for example, when it is compared to a number
+  sum.valueOf = () => x;
+  return sum;
+}

5kyu/a-chain-adding-function/tests.ts

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+import add from './solution';
+import {assert} from "chai";
+
+describe('solution', () => {
+  it('should work when called once', () => {
+    assert(add(1) == 1);
+  });
+  it('should work when called twice', () => {
+    assert(add(1)(2) == 3);
+  });
+  it('should work when called 5 times', () => {
+    assert(add(1)(2)(3)(4)(5) == 15);
+  });
+});