Hello !
Work better like this :
<script type="text/javascript">
(function($) {
$(document).ready(function(){
acf.add_filter('validation_complete', function( json, $form ){
// if empty
if( !$("input#acf-_post_title").val() ) {
var temp = new Object();
temp["input"] = "acf[_post_title]";
temp["message"] = "Le titre est requis";
// if no error
if(json.errors == 0){
// set a new array
json.errors = new Array();
}
// set valid to 0 instead of 1
json.valid = 0;
// push the error
json.errors.push(temp);
}
// return
return json;
});
});
})(jQuery);
</script>
Thank you James for the help !