Programming for beginners: JavaScript: map: Return new array by applying function on every element of the array

map method returns new array with the results of calling a provided function on every element in this array.

Syntax

arr.map(callback[, thisArg])

callback is a function that takes following three arguments.

Argument	Description
currentValue	The current element being processed in the array.
index	The index of the current element being processed in the array.
array	The array that map() is being applied to.

thisArg

Optional. Value to use as this when executing callback.

Get new array by squaring element

/* Get new array by squaring every element */

var arr2 = arr1.map(function(value){

return value * value

});

Get new array by applying square root

var arr3 = arr1.map(Math.sqrt);

map.html

<!DOCTYPE html>

<html>

<head>
    <title>Array map</title>
</head>

<body>
    <script type="text/javascript">
        var arr1 = [2, 3, 5, 7];
        displayArray(arr1);

        /* Get new array by squaring every element */
        var arr2 = arr1.map(function(value) {
            return value * value
        });
        displayArray(arr2);

        /* Get new array by applying square root on every element */
        var arr3 = arr1.map(Math.sqrt);
        displayArray(arr3);

        function displayArray(array, arrayName) {
            document.write("<br />Elements in array " + arrayName + " are <br />");

            array.forEach(function(value) {
                document.write(value + "<br />");
            });
        }
    </script>
</body>

</html>

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Programming for beginners

Saturday, 15 September 2018

JavaScript: map: Return new array by applying function on every element of the array

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