JavaScript: Get all indices of values in an array

JavaScript fundamental (ES6 Syntax): Exercise-216 with Solution

Indices of Value in Array

Write a JavaScript program to get all val indices in an array. If val never occurs, return [].

• Use Array.prototype.reduce() to loop over elements and store indexes for matching elements.

Sample Solution:

JavaScript Code:

// Define a function 'indexOfAll' that takes an array 'arr' and a value 'val' as input
const indexOfAll = (arr, val) =>
  // Use the 'reduce' method to iterate over the elements of the array
  arr.reduce((acc, el, i) => 
    // If the current element equals the value 'val', append its index to the accumulator array 'acc'
    // Otherwise, return the accumulator array 'acc' unchanged
    (el === val ? [...acc, i] : acc), 
    // Set the initial value of the accumulator array 'acc' as an empty array
    []);

// Test the 'indexOfAll' function with sample inputs
console.log(indexOfAll([1, 2, 3, 1, 2, 3], 1));
// Output: [0, 3]
console.log(indexOfAll([1, 2, 3], 4));
// Output: []

Output:

[0,3]
[]

Visual Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-216-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that returns an array of all indices at which a specified value appears in an array.
• Write a JavaScript function that iterates over an array and collects the indices of matching elements.
• Write a JavaScript program that uses a loop to find and return positions of a target value in an array.
• Write a JavaScript function that handles cases where the target value does not occur and returns an empty array.

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