如何在之后提醒 map() 值<option>的<select>已使用 Javascript 选择标签？

Question

I was tasked to use a map to store the names of 5 students with their corresponding average grade. I have initialised this map with fictitious hardcoded names and grades as follows:

const avgGrade = new Map();

avgGrade.set('Kyle', '82%');
avgGrade.set('Sarah', '50%');
avgGrade.set('Skye', '96%');
avgGrade.set('Taylor', '75%');
avgGrade.set('Bantu', '98%');

My goal is to write the JavaScript to display the name of each student in a drop-down menu. When the student's name is selected from the drop-down menu, the student's grade should be displayed using an alert. These are the hints I was given (Hint: Remember that you can use the value and innerHTML attributes of an element.)

I tried doing this, but there is something I'm not getting right. can someone please tell me where I'm going wrong. Here's my code:

//dropdown menu using a for loop 

let dropdown = document.querySelector('#dropdown');
for (i=0; i<avgGrade.length; i++){
let option = document.createElement('option');
option.innerHTML = avgGrade.keys();
dropdown.appendChild(option);
}

//also,I to just alert like this:
function studentGrades()//called the function in select tag on the DOM using the onchange event
{
alert( Select.options[selectedIndex].value + ' average grade is ' + avgGrade.values[i]);
}

Answer 1

You will have to make sure you are iterating Map correctly. You can use forEach() for that. To insert your options please give both text and value .

Variables like Select , i , selectedIndex are not defined in your code.

To get the values from Map , please use standard Map methods like get() .

 const avgGrade = new Map(); avgGrade.set('Kyle', '82%'); avgGrade.set('Sarah', '50%'); avgGrade.set('Skye', '96%'); avgGrade.set('Taylor', '75%'); avgGrade.set('Bantu', '98%'); let dropdown = document.querySelector('#dropdown'); avgGrade.forEach((val, key) => { let option = document.createElement('option'); option.text = key; option.value = key; dropdown.appendChild(option); }); //also,I to just alert like this: function studentGrades(select) { //called the function in select tag on the DOM using the onchange event alert(select.value + ' average grade is ' + avgGrade.get(select.value)); }

 <select id="dropdown" onchange="studentGrades(this)"> </select>

I took the liberty of passing this as an argument on the onChange. You might be doing it some other way.