Check if any input file has been changed

Question

My form has several inputs like this:

<input type="file" name="imagem_file[]" class="form-control">

<button id="btnProdutoImagem" class="btn btn-info btn-block">Cadastrar</button>

And my Jquery checks if the input has been changed like this:

<script>
$(document).ready(function(){
    $("#btnProdutoImagem").on('click', function(){

        var target = $("input[name='imagem_file[]:first']").val();

        if (target.length == 0) {
          console.log('Nenhum arquivo selecionado.');
        }
    })
});
</script>

But this only works if the first input file is changed, if I select according to Jquery does not identify, how to identify if anyone has changed and validate?

If I just leave it at that:

var target = $("input[name='imagem_file[]']").val();

Jquery does not validate either.

Answer 1

With :first you are selecting only the first.

To check all you need to go through the fields to see if any has been filled in. For this you can use .each:

$(document).ready(function(){
    $("#btnProdutoImagem").on('click', function(){

        var target = $("input[name='imagem_file[]']");
        var vazio = true;
        
        target.each(function(i,e){
           if($(e).val()){
              vazio = false;
           }
        });

        if(vazio){
             console.log('Nenhum arquivo selecionado.');
        }

    })
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="file" name="imagem_file[]" class="form-control">
<br>
<input type="file" name="imagem_file[]" class="form-control">
<br>
<input type="file" name="imagem_file[]" class="form-control">
<br>
<button id="btnProdutoImagem" class="btn btn-info btn-block">Cadastrar</button>

Answer 2

You cannot detect changes in input with the change event?

<input id="input-file" type="file" name="imagem_file[]" class="form-control">

<button id="btnProdutoImagem" class="btn btn-info btn-block">Cadastrar</button>

<script>
$(document).ready(function(){
    $("#input-file").on('change', function(){

          alert('Meu arquivo mudou, devo fazer alguma coisa...');

    })
});
</script>