js determine file type and control form submission sample code_javascript skills

The following code implements control form submission

Copy code The code is as follows:

function shangchuan() {

var filepath = document.getElementById("file").value;
alert(filepath);
if(filepath==""){
alert("Please choose to upload file! ");
document.getElementById("file").disabled=true;

}
var extname=filepath.substr(filepath.length-3, filepath.length);
alert("extname::" extname);
//var extname = filepath.substring(filepath.lastIndexOf(".") 1,filepath.length);
// extname = extname.toLowerCase ();//Handling case
if(extname!= "bmp" && extname!= "jpg" && extname!= "gif"){
alert("Only bmp, jpg, gif can be uploaded Format pictures! ");

document.getElementById("file").disabled=true;
}
else{
document.getElementById("file").disabled=false ;
}

}

Copy code The code is as follows:

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Click to upload