Change Find a File Label in Document Library

Hi,

I want to change label Find a file label in Document Library webpart toEx: BookName. Then, i'm using bellow script:

<script type="text/javascript">
setTimeout(function () {
document.getElementById('inplaceSearchDiv_WPQ2_lsinput').placeholder ='Ex:BookName';
document.getElementById('inplaceSearchDiv_WPQ2_lsinput').value= 'Ex:BookName';
}, 800);
</script>

The above code work well on the onload page of the view list library only.

But, when user remove value inside Find a file text, the labeling turn to default'Find a file' .

Thank You.