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(ES6) Avoiding Array Mutations with concat(), slice(), and ...spread
const addCounter = (list) => {
return [...list, 0];
};
const removeCounter = (list, index) => {\
return [
...list.slice(0, index),
...list.slice(index + 1)
];
};
const incrementCounter = (list, index) => {
return [
...list.slice(0, index),
list[index] + 1,
...list.slice(index + 1)
];
};
const testAddCounter = () => {
const listBefore = [];
const listAfter = [0];
deepFreeze(listBefore);
expect(
addCounter(listBefore)
).toEqual(listAfter);
}
const testRemoveCounter = () => {
const listBefore = [0, 10, 20];
const listAfter = [0, 20];
deepFreeze(listBefore);
expect(
removeCounter(listBefore, 1)
).toEqual(listAfter);
};
const testIncrementCounter = () => {
const listBefore = [0, 10, 20];
const listAfter = [0, 11, 20];
deepFreeze(listBefore);
expect(
removeCounter(listBefore, 1)
).toEqual(listAfter);
};
}
testAddCounter();
testRemoveCounter();
testIncrementCounter();
console.log('all tests passed');
<!--
expect for testing:
<script src="https://wzrd.in/standalone/expect@latest"></script>
deepFreeze for not allowing mutations:
<script src="https://wzrd.in/standalone/deep-freeze@latest"></script>
-->
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>JS Bin</title>
<script src="https://wzrd.in/standalone/expect@latest"></script>
<script src="https://wzrd.in/standalone/deep-freeze@latest"></script>
</head>
<body>
</body>
</html>
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