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(ES6) Avoiding Array Mutations with concat(), slice(), and ...spread
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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'); |
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<!-- | |
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> | |
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</html> |
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