Understanding how reduce can be used instead of map and join in this function

user_14104374 0
Viewed 225

I've got the following function that gets all checked checkboxes on my html form with the given element Name. I have a loose understanding that a reduce function can replace the .map and .join sections so was looking for a poke in the right direction of how to implement that and also if there is any other steps I could take to optimise this function?

  function getCheckedValuesOf(elmName){
    return [...document.getElementsByName(elmName)].filter(box=>box.checked==true).map(box=>box.value).join(", ")
  }
reduce arrays javascript
4 Answers

function getCheckedValuesOf(elmName) {
  return [...document.getElementsByName(elmName)]
    // acc is value returned by previous iteration
    // curr is the current iterated element
    .reduce((acc, curr) => {
      // do nothing on unchecked
      if (curr.checked) {
        // add a , only if acc is not empty, to prevent useless starting ,
        acc += (acc !== "" ? ", " : "") + curr.value
      }
      
      // always return acc, or next iteration will have acc === undefined
      return acc;
      
    // second argument of reduce is the initial value of acc
    // if not set then it default to the first element of the array
    // and the iteration starts on the second element
    }, '')
}

document.getElementById("log").onclick = () => console.log(getCheckedValuesOf("name"))
console.log(getCheckedValuesOf("name"))
<input type="checkbox" name="name" checked="false" value="i1"/>i1
<input type="checkbox" name="name" value="i2"/>i2
<input type="checkbox" name="name" checked="false" value="i3"/>i3
<input type="checkbox" name="name" value="i4"/>i4
<input type="checkbox" name="name" checked="false" value="i5"/>i5
<input type="checkbox" name="name" value="i6"/>i6

<button id="log">log</button>

user_101539450

Can you try this one? Let me know if it works.

function getCheckedValuesOf(elmName) {
    return [...document.getElementsByName(elmName)].reduce((a, b) => b.checked && b.value && (a.length>0 ? `${a}, ${b.value}`: `${a} ${b.value}`) || a, "");
}
user_67907440

You can do it with reduce only. modified from @akshaybande 's answer to fix the errors (like leading ", " etc.)

function getCheckedValuesOf(elmName) {
    return [...document.getElementsByName(elmName)].reduce((acc, cur) => {
      if (cur.checked && cur.value){
          return acc.length >= 1 ? `${acc}, ${cur.value}` : `${cur.value}`
      } 
      return acc;
    }, "");
}

document.getElementById("log").onclick = () => console.log(getCheckedValuesOf("name"))
console.log(getCheckedValuesOf("name"))
<input type="checkbox" name="name" checked="false" value="1"/>1
<input type="checkbox" name="name" value="2"/>2
<input type="checkbox" name="name" value="3"/>3
<input type="checkbox" name="name" value="4"/>4
<input type="checkbox" name="name" checked="false" value="5"/>5
<input type="checkbox" name="name" value="6"/>6

<button id="log">log</button>

user_97925940

something like this?

        function getCheckedValuesOf(elmName) {
            return [...document.getElementsByName(elmName)]
                .reduce((str, box) => {
                    if (box.checked == true) {
                        str += box.value +', '
                    }
                    return str;
                }, '');
        }

        document.querySelector('button').onclick = () => {
            console.log(getCheckedValuesOf('input'))
        }
    <input type="checkbox" checked name="input" value="1">
    <input type="checkbox" name="input" value="2">
    <input type="checkbox" name="input" value="3">
    <input type="checkbox" checked name="input" value="4">
    <input type="checkbox" name="input" value="5">
    <button>click</button>

user_121705820
Related