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Negative Indexing in JavaScript Arrays
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| const assert = require('assert'); | |
| const applyNegativeIndex = (array) => { | |
| assert(Array.isArray(array)); | |
| const negativeIndexProxy = new Proxy(array, { | |
| get(target, prop) { | |
| if (!isNaN(prop)) prop = parseInt(prop); | |
| if (prop < 0) prop += target.length; | |
| return Reflect.get(target, prop); | |
| }, | |
| set(target, prop, value) { | |
| if (!isNaN(prop)) prop = parseInt(prop); | |
| if (prop < 0) prop += target.length; | |
| Reflect.set(target, prop, value); | |
| } | |
| }); | |
| return negativeIndexProxy; | |
| }; | |
| // USAGE: | |
| const a = applyNegativeIndex([1, 2, 3, 4]); | |
| console.log(a[-1], a[-2]); // 4 3 | |
| a[-1] = 100; | |
| a[0] = 200; | |
| console.log(a); // [200, 2, 3, 100] |
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