Dynamically update value of a key in Map in JavaScript

Question

I currently have a function below to find the first nonrepeating letter. For example, for the string carro, that letter would be c; for the string total, that letter would be o. I have the following code that works:

function findFirstNonrepeatedChar(str) {
  const store = {};
  const arr = str.split('');

  arr.forEach(item => {
    if(!store[item]) {
      store[item] = 1;
    } else {
      store[item] = store[item] + 1;
    }
  })
  
  for(let char in store) {
    if(store[char] === 1) return char;
  }
}

However, now I want to use a Map instead of just a plain object, and I'm having difficulty to update the frequency of the duplicate word like below:

function findFirstNonrepeatedChar(str) {
  const store = new Map();
  const arr = str.split('');

  arr.forEach(item => {
    if(!store.has(item)) {
      store.set(item, 1);
    } else {
      store[item]++;
    }
  })
  
  console.log(store, 'store')
  for(let char in store) {
    if(store[char] === 1) return char;
  }
}

What would be the best way to do so?

for the string total, that letter would be t, could you confirm this, because t occurs 2 time in total? — hgb123
– hgb123, Commented Jan 21, 2021 at 2:54

hgb123 · Accepted Answer · 2021-01-21 03:50:24Z

1

There are 2 things here:

you set to save the key-value to store, use get to get the value by key
```
store.set(item, (store.get(item) || 0) + 1);
```
you iterate the key-value pairs of Map by for..of, not for..in

function findFirstNonrepeatedChar(str) {
  const store = new Map();
  const arr = str.split("");

  arr.forEach((item) => {
    store.set(item, (store.get(item) || 0) + 1);
  });

  for (let [char, occurrences] of store) {
    if (occurrences === 1) {
      return char;
    }
  }
}

console.log(findFirstNonrepeatedChar("carro"));
console.log(findFirstNonrepeatedChar("total"));

answered Jan 21, 2021 at 3:50

hgb123

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Comments

the_cuaz · Accepted Answer · 2021-01-21 04:02:03Z

0

Here's how I'd do it using Array.prototype.find() if you're interested in alternative solutions.

const findFirstNonrepeatedChar = (str) => str.split('').find(
  (val) => str.match(new RegExp(val, 'g')).length === 1
);

console.log(findFirstNonrepeatedChar('total'));
console.log(findFirstNonrepeatedChar("carro"));
console.log(findFirstNonrepeatedChar("aabbcc"));

answered Jan 21, 2021 at 4:02

the_cuaz

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