Eu optei por esta opção que esclarece como personalizar completamente o botão de navegação, incluindo um manipulador do nome do arquivo enviado, também personalizado. Ele adiciona campos adicionais e controles do lado do cliente, apenas para mostrar como incluir a navegação em um formulário "real", não apenas autônomo.
Aqui está o código de código: http://codepen.io/emiemi/pen/zxNXWR
JS:
//click on our custom btn triggers a click on the hidden actual file input
$("#btnup").click(function(){
$("#fileup").click();
});
//changes on the three fields (input, tit,and name) trigger a control which checks if the 3 fields are all filled and if file field is valid (an image is uploaded)
$('#fileup').change(function(){
var formDOMObj = document.upload;
//here we assign tu our text field #fileup the name of the selected file
var res=$('#fileup').val();
var arr = res.split("\\");
//if file is not valid we show the error icon and the red alert
if (formDOMObj.fileup.value.indexOf(".jpg") == -1 && formDOMObj.fileup.value.indexOf(".png") == -1 && formDOMObj.fileup.value.indexOf(".jpeg") == -1 && formDOMObj.fileup.value.indexOf(".bmp") == -1 && formDOMObj.fileup.value.indexOf(".JPG") == -1 && formDOMObj.fileup.value.indexOf(".PNG") == -1 && formDOMObj.fileup.value.indexOf(".JPEG") == -1 && formDOMObj.fileup.value.indexOf(".BMP") == -1){
$( ".imgupload" ).hide("slow");
$( ".imguploadok" ).hide("slow");
$( ".imguploadstop" ).show("slow");
$('#nomefile').css({"color":"red","font-weight":700});
$('#nomefile').html("The file "+arr.slice(-1)[0]+" is not an image!");
$( "#bottone" ).hide();
$( "#fakebtn" ).show();
}else{
//if file is valid we show the green alert
$( ".imgupload" ).hide("slow");
$( ".imguploadstop" ).hide("slow");
$( ".imguploadok" ).show("slow");
$('#nomefile').html(arr.slice(-1)[0]);
$('#nomefile').css({"color":"green","font-weight":700});
if (formDOMObj.nome.value!=""&&formDOMObj.tit.value!=""&&formDOMObj.fileup.value!=""){
//if all three fields are valid the fake input btn is hidden and the actual one i s finally hown
$( "#fakebtn" ).hide();
$( "#bottone" ).show();
}
}
});
$('#nome').change(function(){
//same as file change but on name field
var formDOMObj = document.upload;
if (formDOMObj.nome.value!=""&&formDOMObj.tit.value!=""&&formDOMObj.fileup.value!=""){
$( "#fakebtn" ).hide();
$( "#bottone" ).show();
}else{
$( "#bottone" ).hide();
$( "#fakebtn" ).show();
}
});
$('#tit').change(function(){
//same as file change but on tit field
var formDOMObj = document.upload;
if (formDOMObj.nome.value!=""&&formDOMObj.tit.value!=""&&formDOMObj.fileup.value!=""){
$( "#fakebtn" ).hide();
$( "#bottone" ).show();
}else{
$( "#bottone" ).hide();
$( "#fakebtn" ).show();
}
});
HTML:
<form name="upload" method="post" action="/" enctype="multipart/form-data" accept-charset="utf-8">
<div class="row">
<div class="col-md-6 center">
<!--this is the actual file input, s hidden beacause we wanna use our custom one-->
<input type="file" value="" class="hidden" name="fileup" id="fileup">
<div class="btn-container">
<!--the three icons: default, ok file (img), error file (not an img)-->
<h1 class="imgupload"><i class="fa fa-file-image-o"></i></h1>
<h1 class="imguploadok"><i class="fa fa-check"></i></h1>
<h1 class="imguploadstop"><i class="fa fa-times"></i></h1>
<!--this field changes dinamically displaying the filename we are trying to upload-->
<p id="nomefile">Only pics allowed! (jpg,jpeg,bmp,png)</p>
<!--our custom btn which triggers the actual hidden one-->
<button type="button" id="btnup" class="btn btn-primary btn-lg">Browse for your pic!</button>
</div>
</div>
<!--additional fields-->
<div class="col-md-6">
<div class="row">
<div class="form-group" id="top">
<div class="col-md-12">
<input type="text" maxlength="100" class="form-control" name="nome" id="nome" placeholder="Your Name">
</div>
</div>
</div>
<div class="row">
<div class="form-group">
<div class="col-md-12">
<input type="text" maxlength="50" class="form-control" name="tit" id="tit" placeholder="I am rubber, you are glue">
</div>
</div>
</div>
<div class="row">
<div class="col-md-8">
<p class="white">All fields are mandatory</p>
</div>
<div class="col-md-4">
<!--the defauld disabled btn and the actual one shown only if the three fields are valid-->
<input type="submit" value="Submit!" class="btn btn-primary" id="bottone" style="padding-left:50px; padding-right:50px; display:none;">
<button type="button" class="btn btn-default" disabled="disabled" id="fakebtn" style="padding-left:40px; padding-right:40px;">Submit! <i class="fa fa-minus-circle"></i></button>
</div>
</div>
</div>
</div>
