Add JavaScriptTwoSum.md

Author: Superklok

JavaScriptTwoSum.md

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+# JavaScript Two Sum
+
+## Challenge:
+
+Given an array of integers `nums` and an integer `target`, return indices of the two numbers such that they add up to `target`.
+
+You may assume that each input would have exactly one solution, and you may not use the same element twice.
+
+You can return the answer in any order.
+
+### 1<sup>st</sup> Example:
+
+`Input: nums = [2,7,11,15], target = 9`
+<br/>
+`Output: [0,1]`
+<br/>
+`Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].`
+
+### 2<sup>nd</sup> Example:
+
+`Input: nums = [3,2,4], target = 6`
+<br/>
+`Output: [1,2]`
+
+### 3<sup>rd</sup> Example:
+
+`Input: nums = [3,3], target = 6`
+<br/>
+`Output: [0,1]`
+
+### Constraints:
+
+`2 <= nums.length <= 10⁴`
+<br/>
+`-10⁹ <= nums[i] <= 10⁹`
+<br/>
+`-10⁹ <= target <= 10⁹`
+<br/>
+Only one valid answer exists.
+
+## Solution:
+
+`const twoSum = (nums, target) => {`
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`let numsObject = {};`
+<br/>
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`for(let i = 0; i < nums.length; i++) {`
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`let n = nums[i],`
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`compliment = target-n;`
+<br/>
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`if (numsObject.hasOwnProperty(compliment)) {`
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`return [i,numsObject[compliment]];`
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`}`
+<br/>
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`numsObject[n] = i;`
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`}`
+<br/>
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;`return [-1,-1];`
+<br/>
+`};`
+<br/>
+<br/>