Update HTML using two values from array of objects

Question

I have an array of objects, each with an age and balance property.

I have a form with a self-select field and a function to loop through and populate the self-select with all of the balances.age values.

<form id="myForm">
  <select id="selectAge">
    <option>Age</option>
  </select>
</form>

var balances = [
    {
        age: 23,
        balance: 10000
    },
    {
        age: 25,
        balance: 24000
    }
]

function getAge(){    
  for(var i = 0; i < balances.length; i++) {
    var opt = balances[i].age;
    var el = document.createElement("option");
    el.text = opt;
    el.value = opt;
    select.add(el);
  }  
}

I'd like to use the selected age value and insert the corresponding balances of the array into some HTML below.

<h2>You should have $<span id="insertBalance"></span>.</h2>

I'm not getting anywhere with this and may have approached this wrong to begin with. How can I find the correct balance for each selected age and display it in my document?

ggorlen · Accepted Answer · 2020-01-02 00:45:38Z

2

You're pretty close. Add an event listener to the dropdown menu to listen for changes. When a change occurs, perform a linear search on the balances array using find to match the event.target.value, which is the selected age.

Note that linear searching is slow, so if the search turns into a bottleneck, you may wish to transform the balances array into an object or Map with age->balance pairs.

const balances = [
  {
    age: 23,
    balance: 10000
  },
  {
    age: 25,
    balance: 24000
  }
];

const selectEl = document.getElementById("select-age");
const balanceEl = document.getElementById("insert-balance");

for (const e of balances) {
  const opt = document.createElement("option");
  selectEl.appendChild(opt);
  opt.text = e.age;
  opt.value = e.age;
}

selectEl.addEventListener("change", event => {
  const found = balances.find(e => e.age == event.target.value);
  balanceEl.innerText = found ? found.balance : "";
});

<select id="select-age">
  <option>Age</option>
</select>
<h2>You should have $<span id="insert-balance"></span>.</h2>

answered Jan 2, 2020 at 0:45

ggorlen

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1 Comment

BigD Over a year ago

So simple! Thanks for taking a look. Confirming this has worked for me.

Mister Jojo · Accepted Answer · 2020-01-02 01:22:33Z

0

const myForm    = document.getElementById('my-form')
  ,   balanceEl = document.getElementById("insert-balance")
  ,   balances  = [ { age: 23, balance: 10000 }, { age: 25, balance: 24000 } ] 
  ;
balances.forEach((elm,i)=>
  {
  myForm.selectAge.options[i] = new Option(elm.age, elm.balance)
  })
myForm.oninput=_=>  
  {
  balanceEl.textContent = myForm.selectAge.value
  }
myForm.onsubmit=e=> 
  {
  e.preventDefault()   // disable form submit
  }
balanceEl.textContent = myForm.selectAge.value

<form action="xxx" method="POST" id="my-form">
  <select name="selectAge">
    <optgroup label="Age">
  </select>
</form>

<h2>You should have $<span id="insert-balance"></span>.</h2>

answered Jan 2, 2020 at 1:22

Mister Jojo

22.9k6 gold badges28 silver badges45 bronze badges

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