表单验证无效-JavaScript

Question

I am trying to implement form validation so that when the submit button is hit, all required fields are filled. here is my code:

function checkInput()
{
    <!--check if these input values are provided -->
    var inputFile = document.getElementByID('inputFile').value;
    var numThreads = document.getElementById('numThreads').value;
    var scoreThresh = document.getElementById('scoreThresh').value;
    var scorePen = document.getElementById('scorePenalty').value;

    if(inputFile==="" ||numThreads==="" ||scoreThresh==="" ||scorePen==="" )
    {
        alert('Please fill in all required fields');

    }

//how i decalare the form

 <form  method =POST id="weVoteForm" onsubmit="return checkInput()">

this code isnt working however. Can anyone clarify what is wrong? Thanks!

Answer 1

You need to call the checkInput function before submitting the form. For this you can use onsubmit event in the form element as.

<form method="POST" id="weVoteForm" onsubmit="return checkInput();">
</form>

Your function should look like this

function checkInput()
{

    //check if these input values are provided -->
    // notice not <!-- in JS for comment and Id not ID
    var inputFile = document.getElementById('inputFile').value;
    var numThreads = document.getElementById('numThreads').value;
    var scoreThresh = document.getElementById('scoreThresh').value;
    var scorePen = document.getElementById('scorePenalty').value;

    if(inputFile==="" ||numThreads==="" ||scoreThresh==="" ||scorePen==="" )
    {
        alert('Please fill in all required fields');
        return false;
    }
  return true;
}

Moreover you can set required attribute in each element without having you to write this code as.

<input type="text" required />