Rain Lover Posted March 5, 2019 Share Posted March 5, 2019 (edited) Scenario Every semester my students need to take at least one test. The following form gives the right average grade of a student: <!DOCTYPE html> <html lang="en"> <head> <title>Average Grade</title> </head> <body> <form> Math: <input type="number" id="test1"> <input type="number" id="test2"> <input type="number" id="test3"> <output id="average"></output> <br> <input type="button" value="Calculate" id="calcBtn"> </form> <script> document.getElementById('calcBtn').addEventListener('click', function() { var test1 = document.getElementById('test1').value; var test2 = document.getElementById('test2').value; var test3 = document.getElementById('test3').value; var average = document.getElementById('average'); average.value = (Number(test1)+Number(test2)+Number(test3)) / 3; }); </script> </body> </html> DEMO The problem is it works right only if all the fields are edited. If the student doesn't take some tests, the average grade won't show the right value. I know it's because of dividing by the fixed number 3 when it calculates the average grade: average.value = (Number(test1)+Number(test2)+Number(test3)) / 3; Question What is a simple approach to get the number of changed input fields? Edited March 5, 2019 by Rain Lover Link to comment Share on other sites More sharing options...
justsomeguy Posted March 5, 2019 Share Posted March 5, 2019 Test each input you get and put any non-empty inputs into an array. Then you can sum the array elements and divide by the array length. 1 Link to comment Share on other sites More sharing options...
merazgasalim Posted March 14, 2019 Share Posted March 14, 2019 Try this <!DOCTYPE html> <html lang="en"> <head> <title>Average Grade</title> </head> <body> <form> Nubmer Of tests:<input type="number" id="nbr" value="0" min="0" max="3"> Math: <input type="number" id="test1" disabled> <input type="number" id="test2" disabled> <input type="number" id="test3" disabled> <output id="average"></output> <br> <input type="button" value="Calculate" id="calcBtn"> </form> <script> var testNbr = document.getElementById('nbr').value; document.getElementById('nbr').addEventListener('input', function() { testNbr = document.getElementById('nbr').value; switch(testNbr){ case '1' : document.getElementById('test1').disabled = false; document.getElementById('test2').disabled = true; document.getElementById('test3').disabled = true; document.getElementById('test2').value = 0; document.getElementById('test3').value = 0; break; case '2' : document.getElementById('test1').disabled = false; document.getElementById('test2').disabled = false; document.getElementById('test3').disabled = true; document.getElementById('test3').value = 0; break; case '3' : document.getElementById('test1').disabled = false; document.getElementById('test2').disabled = false; document.getElementById('test3').disabled = false; break; default: document.getElementById('test1').disabled = true; document.getElementById('test2').disabled = true; document.getElementById('test3').disabled = true; } }); document.getElementById('calcBtn').addEventListener('click', function() { var test1 = document.getElementById('test1').value; var test2 = document.getElementById('test2').value; var test3 = document.getElementById('test3').value; var average = document.getElementById('average'); average.value = (Number(test1)+Number(test2)+Number(test3)) / testNbr; }); </script> </body> </html> Link to comment Share on other sites More sharing options...
dsonesuk Posted March 15, 2019 Share Posted March 15, 2019 <!DOCTYPE html> <html lang="en"> <head> <title>Average Grade</title> </head> <body> <form id="myform"> Math: <input type="number" id="test1"> <input type="number" id="test2"> <input type="number" id="test3"> <output id="average"></output> <br> <input type="button" value="Calculate" id="calcBtn"> </form> <script> document.getElementById('calcBtn').addEventListener('click', function() { var myformelem = document.getElementById('myform'); var answeredArr = []; var total=0; for(i=0;i<myformelem.length;i++){ if(myform.elements[i].value != myform.elements[i].defaultValue && myform.elements[i].id != "calcBtn"){ answeredArr.push(myform.elements[i].value); total += parseInt(answeredArr[i]); } } document.getElementById('average').innerHTML=(total/(answeredArr.length)).toFixed(2); /*var test1 = document.getElementById('test1').value; var test2 = document.getElementById('test2').value; var test3 = document.getElementById('test3').value; average.value = (Number(test1)+Number(test2)+Number(test3)) / 3;*/ }); </script> </body> </html> Like mentioned the array can store values to add together for total, then use array again to identify the number answered to divide by for average. Link to comment Share on other sites More sharing options...
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