Does javascript array have map method?

Javascript arrays have map methods. In JavaScript, the map() method of an array is used to call the specified callback function on each element of the array and return an array containing the results; the syntax format is "array.map(callback function, thisValue);". The map() method will return a new array, where each element is the callback function return value of the associated original array element; for each element in the array, the map() method will call the callback function once (in ascending index order) .

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

Javascript arrays have map methods.

javascript array map() method

The map() method can call the specified callback function for each element of the array. Process and return an array containing the results.

The map() method processes elements sequentially in the order of the original array elements.

Syntax

array.map(function(currentValue,index,arr), thisValue)

##ParametersDescriptionOptional. The object is used as the execution callback, passed to the function, and used as the value of "this".

function(currentValue, index,arr)	Required. Function, each element in the array will execute this function. Function parameters: currentValue is required. The value of the current element #index is optional. The index value of the current element #arr Optional. The array object to which the current element belongs
thisValue	If thisValue is omitted, or null or undefined is passed in, then the this of the callback function is the global object.

The map() method returns a new array where each element is the callback function return value of the associated original array element. The map() method calls the callback function once for each element in the array (in ascending index order) and does not call the callback function for missing elements in the array.

In addition to array objects, the map() method can be used by any object with a length property and an indexed property name, such as an Arguments parameter object.

Let’s learn more about it through code examples:

Example 1
##The following example uses the map() method to map an array and convert the array into The value of each element in is squared, multiplied by the PI value, the area value of the returned circle is used as the element value of the new array, and finally the new array is returned.

function f (radius) {
    var area = Math.PI * (radius * radius);
    return area.toFixed(0);
}
var a = [10,20,30];
var a1 = a.map(f);
console.log(a1);

Example 2

The following example uses the map() method to map an array and divide the value of each element in the array by A threshold, and then returns this new array where both the callback function and the threshold exist as properties of the object. This method demonstrates how to use the thisArg parameter in the map.

var obj = {
    val : 10,
    f : function (value) {
        return value % this.val;
    }
}
var a = [6,12,25,30];
var a1 = a.map(obj.f, obj);
console.log(a1);  //6,2,5,0

Example 3

The following example demonstrates how to use JavaScript built-in methods as callback functions.

var a = [9, 16];
var a1 = a.map(Math.sqrt);
console.log(a1);  //3,4

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