限制文件上传格式

1.直接上代码：

 function checkFile(img) {
    let file = img;
    console.log(img);
    if (file == null || file == "") {
        successText.innerHTML = "请选择要上传的文件!";
            keepSuccess.style.height = '200px';
            inputReadOnly();
            okBtn.addEventListener('click', function() {
                keepSuccess.style.height = 0;
                inputChange();
            })
        return false;
    }
    //定义允许上传的文件类型
    var allow_ext = ".jpg|.png|.gif";
    //提取上传文件的类型
    var ext_name = file.substring(file.lastIndexOf("."));
    //判断上传文件类型是否允许上传
    if (allow_ext.indexOf(ext_name + "|") == -1) {
        successText.innerHTML =  "该文件不允许上传，请上传" + allow_ext + "类型的文件,当前文件类型为：" + ext_name;
            keepSuccess.style.height = '200px';
            inputReadOnly();
            okBtn.addEventListener('click', function() {
                keepSuccess.style.height = 0;
                inputChange();
            })
        return false;
    }
}

这是封装的判断文件是图片的函数；

2.接口调用该函数：

function fileChange() {
    var formData = new FormData();
    let headname=$('#file')[0].value;
    let ishead=checkFile(headname);
   if(ishead!=false){
       let changemyhead=new Promise((resolve,reject)=>{
           formData.append('profile1', $('#file')[0].files[0]);
           formData.append('account', sessionStorage.getItem("account"));
           resolve();
       });
       changemyhead.then(()=>{
           $.ajax({
               // 类型
               type: "POST",
               url: "http://localhost:8080/ToSkyNews_war_exploded/saveUserProfile",
               data: formData,
               dataType: "json",
               contentType: false,
               processData: false,
               success: function(date) {
                   console.log(date);
                   if (date.message == "成功并返回数据") {
                       successText.innerHTML = '上传头像成功！!';
                       keepSuccess.style.height = '200px';
                       inputReadOnly();
                       okBtn.addEventListener('click', function() {
                           keepSuccess.style.height = 0;
                           inputChange();
                       })
                   } else {
                       successText.innerHTML = '上传头像失败，请重试！';
                       keepSuccess.style.height = '200px';
                       inputReadOnly();
                       okBtn.addEventListener('click', function() {
                           keepSuccess.style.height = 0;
                           inputChange();
                       })
                   }
                   console.log(date.data.file.data);
                   changeHead.style.backgroundImage = `url(${date.data.file.data})`;
                   for (let i = 0; i < userHead.length; i++) {
                       userHead[i].style.backgroundImage = `url(${date.data.file.data})`;
                   }
               },
               error: function(returndata) {
                   console.log(returndata);
               }
           })
       })
   }
}