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How to map, reduce and filter a Set element using JavaScript ?
  • Last Updated : 08 May, 2020

The map(), reduce() and filter() are array functions that transform the array according to the applied function and return the updated array. They are used to write simple, short and clean codes for modifying an array instead of using the loops.

  • map() method: It applies a given function on all the elements of the array and returns the updated array. It is the simpler and shorter code instead of a loop. The map is similar to the following code:




    arr = new Array(1, 2, 3, 6, 5, 4);
    for(int i = 0; i < 6; i++) {
        arr[i] *= 3;
    }

    Syntax:

    array.map(function_to_be_applied)
    array.map(function (args) {
        // code;
    })
    

    Example:




    function triple(n){
        return n*3;
    }    
    arr = new Array(1, 2, 3, 6, 5, 4);
      
    var new_arr = arr.map(triple)
    console.log(new_arr);
    Output: 
    [ 3, 6, 9, 18, 15, 12 ]
    
  • reduce() method: It reduces all the elements of the array to a single value by repeatedly applying a function. It is an alternative of using a loop and updating the result for every scanned element. Reduce can be used in place of the following code:




    arr = new Array(1, 2, 3, 6, 5, 4);
    result = 1
    for(int i = 0; i < 6; i++) {
        result = result * arr[i];
    }

    Syntax:

    array.reduce(function_to_be_applied)
    array.reduce(function (args) {
        // code;
    })
    

    Example:






    function product(a, b){
        return a * b;
    }
    arr = new Array(1, 2, 3, 6, 5, 4);
      
    var product_of_arr = arr.reduce(product)
    console.log(product_of_arr)

    Output:

    720
  • filter() method: It filters the elements of the array that return false for the applied condition and returns the array which contains elements that satisfy the applied condition. It is a simpler and shorter code instead of the below code using a loop:




    arr = new Array(1, 2, 3, 6, 5, 4);
    new_arr = {}
    for(int i = 0; i < 6; i++) {
        if(arr[i] % 2 == 0) {
             new_arr.push(arr[i]);           
        }
    }

    Syntax:

    array.filter(function_to_be_applied)
    array.filter(function (args) {
        // condition;
    })
    

    Example:




    arr = new Array(1, 2, 3, 6, 5, 4);
    var new_arr = arr.filter(function (x){
        return x % 2==0;
    });
      
    console.log(new_arr)

    Output:

    [ 2, 6, 4 ]
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