add js solution for findTargetSumWays

problems/0494.目标和.md

@@ -306,6 +306,36 @@ func findTargetSumWays(nums []int, target int) int {
 }
 ```
 
+Javascript：
+```javascript
+const findTargetSumWays = (nums, target) => {
+
+    const sum = nums.reduce((a, b) => a+b);
+
+    if(target > sum) {
+        return 0;
+    }
+
+    if((target + sum) % 2) {
+        return 0;
+    }
+
+    const halfSum = (target + sum) / 2;
+    nums.sort((a, b) => a - b);
+
+    let dp = new Array(halfSum+1).fill(0);
+    dp[0] = 1;
+
+    for(let i = 0; i < nums.length; i++) {
+        for(let j = halfSum; j >= nums[i]; j--) {
+            dp[j] += dp[j - nums[i]];
+        }
+    }
+
+    return dp[halfSum];
+};
+```
+
 
 
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