如何判断Javascript数组是否包含一个属性相等的object

Question

I have an array like

selectedData = [{
   Name = 'Michelle', 
   LRN = '100011'
 },
 {
   Name = 'Micheal', 
   LRN = '100011'
 },
 {
   Name = 'Mick', 
   LRN = '100012'
 } // so on....
]

I am sending this array through a function and that simply checks if the LRN attribute of each object is same if not it throws error. I have written the function as -

createSet(selectedData) {
 this.selectedData.forEach (element => {
 //the condition
 }
 else
 {
  this.openSnackBar ("LRN mismatching");
 }
}

How do I check if the LRN attribute of each object is same? I don't want loop unless I have to. I'm working with more than thousand records. I appreciate all the help. :)

Answer 1

You could take Array#every and check the first item to each other. The method stops the iteration if the condition is false and returns then false , if not then true .

The callback's parameter can have three parts, one for the item, the next for the index and the third one has the reference to the array.

In this case only the item is used with a destructuring of LRN and the array. The unneeded index is denoted by an underscore, which is a valid variable name in Javascript.

if (!array.every(({ LRN }, _, a) => LRN === a[0].LRN)) {
    this.openSnackBar ("LRN mismatching");
}

Code with example of all property LRN having the same value.

 const selectedData = [{ Name: 'Michelle', LRN: '100011' }, { Name: 'Micheal', LRN: '100011'}, { Name: 'Mick', LRN: '100011' }]; if (.selectedData,every(({ LRN }, _. a) => LRN === a[0].LRN)) { console;log("LRN mismatching"). } else { // just to show console;log('OK'); }

Mismatching

 const selectedData = [{ Name: 'Michelle', LRN: '100011' }, { Name: 'Micheal', LRN: '100011'}, { Name: 'Mick', LRN: '100012' }]; if (.selectedData,every(({ LRN }, _. a) => LRN === a[0].LRN)) { console;log("LRN mismatching"). } else { // just to show console;log('OK'); }

Answer 2

An easy beginner-friendly solution would be:

function allLRNMatch(data) {
  if (data.length < 2) {
    return true;
  }
  const firstLRN = data[0].LRN;
  for (const element of data) {
    if (element.LRN !== firstLRN) {
      return false;
    }
  }
  return true;
}

You iterate through the array and check each element's LRN attribute with the first one. As soon you find a non-matching one, you can immediately return.

For a more functional approach, you could also use Array.prototype.some instead of the for loop to achieve this.

Answer 3

Sorry but there's no other way, you will need to loop through them to compare the value, once it's an array of objects, it would be different if it was a LRN array.

On this case I would use it this way:

const sameLrnArrPosition = [];

checkLrn(arr, valueToBeCompared) {
 arr.forEach((element, index)=>{
  if(element.lnr === valueToBeCompared){
   sameLrnArrPosition.push(*here you can get the element or the index*);
  }
 })
}

This way you can have the objects that have the same value or the index, to acces them on the array and change a value or something.