Question 50280 in Javascript Question posted in
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How to replace one element of array inside loop – Javascript

There is an array arr = [1, 2, "a", 4, 5];. Using loop (for…of) every element of array must be pushed inside another empty array result = [];.

But, inside arr there is an element that needed to be replaced inside loop. Here, we need to replace string "a" with number 3 and than push it inside array result.

In the end we need to get an array result = [1, 2, 3, 4, 5];. As you can see string "a" was replaced and instead number 3 was pushed.

!Important initial array arr shouldn’t be mutated and loop is a required condition.

Example:

const arr = [1, 2, "a", 4, 5];
const result = [];

for(let elem of arr) {
  if(typeof elem === "string") {
    // changing elem to number 3 and pushing it into result array instead of "a"
  }
// ...
}

Tried use several different array methods, but it didn’t help.

Tags:

3

Answers


  1. 0

    You can replace the string "a" with the number 3 and push every element into a new array using the for…of loop as follows:

    const arr = [1, 2, "a", 4, 5];
const result = [];

for (let elem of arr) {
  if (typeof elem === "string" && elem === "a") {
    // replace "a" with number 3 and push it into the result array
    result.push(3);
  } else {
    // push the current element into the result array
    result.push(elem);
  }
}

console.log(result); // [1, 2, 3, 4, 5]
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  2. 0

    Just use an Array.map

    here 3 each time

    const arr = [1, 2, "a", 4, 5, "b"];
const result = arr.map(item => typeof item === "string" ? 3 : item)
console.log(result)

    Here index+1

    const arr = [1, 2, "a", 4, 5, "b"];
const result = arr.map((item, i) => typeof item === "string" ? i + 1 : item)
console.log(result)
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  3. 0

    You may want to use Array.reduce here. Something like:

    const reducer = (acc, v, i) => 
  [...acc, isNaN(+v) ? (acc[i-1] || 0) + 1 : +v];

const arr = [1, 2, "a", 4, 5];
const result = arr.reduce(reducer, []);
console.log(`in: ${JSON.stringify(arr)}`);
console.log(`out: ${JSON.stringify(result)}`);

const arr2 = ["b", 2, "a", 4, 5];
const result2 = arr2.reduce(reducer, []);
console.log(`in: ${JSON.stringify(arr2)}`);
console.log(`out: ${JSON.stringify(result2)}`);

const arr3 = ["b", 2, "a", 4, "5"];
const result3 = arr3.reduce(reducer, []);
console.log(`in: ${JSON.stringify(arr3)}`);
console.log(`out: ${JSON.stringify(result3)}`);

// or in increments by choice
const reducerFactory = step => (acc, v, i) => 
  [...acc, isNaN(+v) ? (acc[i-1] || 0) + step : +v];

const arr4 = ["b", 4, "a", 8, 10, "12"];
const result4 = arr4.reduce(reducerFactory(2), []);
console.log(`in: ${JSON.stringify(arr4)}`);
console.log(`out: ${JSON.stringify(result4)}`);
    .as-console-wrapper {
    max-height: 100% !important;
}
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