JavaScript ，Array map 方法

map 方法 (Array) (JavaScript)

对数组的每个元素调用定义的回调函数并返回包含结果的数组。

array1.map(callbackfn[, thisArg])

参数

返回值

异常

备注

示例

JavaScript

// Define the callback function.
function AreaOfCircle(radius) {
    var area = Math.PI * (radius * radius);
    return area.toFixed(0);
}

// Create an array.
var radii = [10, 20, 30];

// Get the areas from the radii.
var areas = radii.map(AreaOfCircle);

document.write(areas);

// Output:
// 314,1257,2827

this 关键字可引用的对象。

JavaScript

// Define an object that contains a divisor property and
// a remainder function.
var obj = {
    divisor: 10,
    remainder: function (value) {
        return value % this.divisor;
    }
}

// Create an array.
var numbers = [6, 12, 25, 30];

// Get the remainders.
// The obj argument specifies the this value in the callback function.
var result = numbers.map(obj.remainder, obj);
document.write(result);

// Output:
// 6,2,5,0

在下面的示例中，内置 JavaScript 方法用作回调函数。

JavaScript

// Apply Math.sqrt(value) to each element in an array.
var numbers = [9, 16];
var result = numbers.map(Math.sqrt);

document.write(result);
// Output: 3,4

下面的示例阐释了这一点。

JavaScript

// Define the callback function.
function threeChars(value, index, str) {
    // Create a string that contains the previous, current,
    // and next character.
    return str.substring(index - 1, index + 2);
}

// Create a string.
var word = "Thursday";

// Apply the map method to the string.
// Each array element in the result contains a string that
// has the previous, current, and next character.
// The commented out statement shows an alternative syntax.
var result = [].map.call(word, threeChars);
// var result = Array.prototype.map.call(word, threeChars);

document.write(result);

// Output:
// Th,Thu,hur,urs,rsd,sda,day,ay

要求

版本信息。

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