Utilities function for JavaScript

findAllIndexesOf.js

/**
 * 
 * @param {*} arr array to search
 * @param {*} val single element to search in array
 * @returns 
 */
function findAllIndexesOf(arr, val) {
    var indexes = [], i;
    for(i = 0; i < arr.length; i++)
        if (arr[i] === val)
            indexes.push(i);
    return indexes;
}

/**
 * e.g.
 * 
 * arr = [ 'a', ' ', 'b', 'c', 'b' ]
 * val = 'b'
 * getAllIndexes(arr, val)-> [ 2, 4 ]
 */

randIdxArrayByLength.js

/**
 * 
 * @param {number} length length of object
 * @param {number} n length of index to generate
 * @returns 
 */
const randIdxArrayByLength = (length, n)=>{
    const res = Array.from({length:n},(item, index)=> index).sort(() => Math.random() - 0.5).slice(0,n);
    return res
}
// e.g.
// console.log(randIdxArrayByLength(5, 3));
// [ 1, 0, 2 ]