array.js

// 1
const indexOf = (arr, item) =>  arr.indexOf(item);
    
   


indexOf([1,2,3,4], 3) 
indexOf([5,6,7,8], 8) 
indexOf([1,2,3,4], 5) 

// 2
const sum = (arr) => {
    return arr.reduce((curr, next) => curr + next);
}

// 3

const remove = (arr, item) => {
    return arr.filter(data => data != item);
  }

// 4

const append = (arr, item) => {
     arr.push(item);
     return arr;
  }

  //5
  const truncate = (arr) => {
    arr.pop();
    return arr;
}

// 6
const prepend = (arr, item) => {
    arr.unshift(item)
    return arr;
}

// 7
const curtail = (arr) => {
    arr.shift();
    return arr;
}

// 8
const insert = (arr, item, index) => {
    arr.splice(index, 0, item) 
    return arr;  
}

// 9
const count = (arr, item) => {
    return arr.filter(data => data == item).length;
    
}

// 10

const duplicates = (arr) => {
    const result = [];
    for(let i = 0; i < arr.length; i++) {
        const value = Math.abs(arr[i]);
        if(arr[value - 1] < 0) {
            result.push(value);
        } else {
            arr[value - 1] *= -1;
        }
    }
    return result;
}