[Vuejs]-Send base64 string data to server but receive empty form value

Ok, after some research I realize the “scope” issue.
function getBase64 returns a Promise and have to handle the value inside the scope, so I move the axios.post in the Promise and I finally see the base64 value in Go program. Problem solved.

modified front-end code:

var myForm = document.getElementById('myForm')
var formData = new FormData(myForm)

var imgBase64 = getBase64(//image-url//)
imgBase64.then(function (res) {
   formData.append('image', res)

   axios.post(' //go-app-engine-service// ', formData)
     .then(res => {
        console.log(res)
     })
     .catch(error => {
        console.log(error)
     })
}