Javascript simple array creation 97% faster
\nRuntime: 80 ms, faster than 97.47% of JavaScript online submissions for Concatenation of Array.\nMemory Usage: 41.6 MB, less than 86.40% of JavaScript online 
```\nRuntime: 80 ms, faster than 97.47% of JavaScript online submissions for Concatenation of Array.\nMemory Usage: 41.6 MB, less than 86.40% of JavaScript online submissions for Concatenation of Array.\n```\n\n```\nvar getConcatenation = function(nums) {\n    let n = nums.length;\n\t\n\t// create return array ans of length 2n\n    let ans = new Array(2*n);\n    \n    for(let i = 0; i < n; i++) {\n\t\t// ans[i] == nums[i] and ans[i + n] == nums[i]\n        ans[i] = ans[i + n]= nums[i];\n    }\n    return ans;\n};\n```
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