# 48. search first index with Binary Search(possible duplicate array)

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medium - accepted / - tried

This is a variation of 37. implement Binary Search (unique).

Your are given a sorted ascending array of number, but **might have duplicates**, you are asked to return the **first index** of a target number.

If not found return -1.

*note*

Please don't use `Array.prototype.indexOf()`

, it is not our goal.