Getting an error with the click function in Javascript

Question

I am building an application that takes in grade and then gives the average. It also has a sort button that makes it so you can sort by the last name of the student entered and a clear button to clear the current values that are in the display array. Here is the code I have so far for the javascript file:

var $ = function (id) {return document.getElementById(id);}
"use strict";

var scoreArray = [];
var dispArray = []; 

var displayScores = function () {
var totalScore = 0;
var numberOfScores = 0;
var averageScore = 0;

numberOfScores = scoreArray.length;

//loop to find the total score 
for (var i=0;i<numberOfScores;i++)
{
totalScore = totalScore + scoreArray[i];
}

//find the average 
averageScore = totalScore/numberOfScores;

var st="";

//put the string in the display array
for(var i=0; i<numberOfScores;i++)
{
st += (dispArray[i]+"\n");
}

//display the average score 
$("#average_score").val(averageScore.toString());

$("#scores").val(st);
};


$("#add_button").click(function(){
var scoreNumber = parseInt( $("#score").val());
var scoreString = $("#last_name").val() + ", " + $("first_name").val() + ": " + $("#score").val();

scoreArray.push(scoreNumber);

dispArray.push(scoreString);

displayScores();

//reset the values 
$("#first_name").val("");
$("#last_name").val("");
$("#score").val("");
$("#first_name").focus();

});

//function to clear the contents of the form
$("#clear_button").click(function(){

//empty the arrays 
scoreArray=[];
dispArray=[];

//reset the values in the form 
$("#scores").val("");
$("#first_name").val("");
$("#last_name").val("");
$("average_score").val("");
$("#score").val("");

});

//function to sort the scores based on the last name that was entered
$("#sort_button").click(function(){
var mylen = scoreArray.length;

//sorting
for(var kk=0;kk<mylen;kk++)
{
    for(var aa = 1; aa<(mylen-kk);aa++)
    {
        var xp1 = dispArray[aa-1].split(" ");
        var lname1 = xp1[0];
        lname1 = lname1.slice(0, -1);

        var xp2 = dispArray[aa].split(" ");
        var lname2 = xp2[0];
        lname2 = lname2.slice(0, -1);

        if (lname1 > lname2){
            var tp1 = scoreArray[aa];
            scoreArray[aa]=scoreArray[aa-1];
            scoreArray[aa-1] = tp1;

            var tp2 = dispArray[aa];
            dispArray[aa]=dispArray[aa-1];
            dispArray[aa-1] = tp2;
        }
    }
}

//display the scores 
$("#scores").val("");
var st=" ";
for(var i=0;i<dispArray.length;i++)
{
    st += (dispArray[i]+"\n");
}

//display the sorted scores 
$("scores").val(st);
});

$("#first_name").focus();

It is giving the error: Uncaught TypeError: Cannot read property 'click' of null at scores.js:38

Line 38 is the click function for the add button to add the score to the display array: $("#add_button").click(function(){

Any thoughts on this?

try debugging, console.log or alert at function start and return false, so that rest does not work, and see if error occurs, if not then see all 3 values by consolelog,if they are fine — Ahmed Sunny
– Ahmed Sunny, Commented Dec 15, 2019 at 20:28
My first guess would be that you are importing your script before the DOM elements you are trying to get are created. Simple fix : load your script at the end of your body, or run it when the document is ready (with a listener) — Seblor
– Seblor, Commented Dec 15, 2019 at 20:30

Mitya · Accepted Answer · 2019-12-16 09:47:19Z

3

This is happening because you've defined $ as a function which returns the result of document.getElementById().

What you've not accounted for is what happens if this operation finds no element, in which case it returns null, and there is no .click() method of null.

In short: your selector #add_button seems not to be finding the intended element. So check your DOM, and the presence of the element, before running that line. Always suspect your selectors. Either that or build in a check that only goes to .click() on finding an element successfully.

let el = $('#add_button');
if (el) el.click(...);

edited Dec 16, 2019 at 9:47

answered Dec 15, 2019 at 20:28

Mitya

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1 Comment

mildlylost Over a year ago

var $ = function (id) { return document.getElementById(id); };

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