javascript Array数组对象简介

2019-04-20174次阅读Arrayjavascript

JavaScript的Array对象是用于构造数组的全局对象,数组是类似于列表的高阶对象。

.concat

无突变

描述

concat() 方法用于合并两个或多个数组。此方法不会更改现有数组,而是返回新数组

Array.prototype.concat ( [ item1 [ , item2 [ , … ] ] ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/concat

例子

var array1 = ['a', 'b', 'c'];
var array2 = ['d', 'e', 'f'];

console.log(array1.concat(array2));
// expected output: Array ["a", "b", "c", "d", "e", "f"]

.copyWithin()

变异

描述

copyWithin() 方法浅复制数组的一部分到同一数组中的另一个位置,并返回它,而不修改其大小,会修改原数组

arr.copyWithin(target)
arr.copyWithin(target, start)
arr.copyWithin(target, start, end)

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/copyWithin

例子

var array1 = ['a', 'b', 'c', 'd', 'e'];

// copy to index 0 the element at index 3
console.log(array1.copyWithin(0, 3, 4));
// expected output: Array ["d", "b", "c", "d", "e"]

// copy to index 1 all elements from index 3 to the end
console.log(array1.copyWithin(1, 3));
// expected output: Array ["d", "d", "e", "d", "e"]

.entries()

无突变

描述

entries() 方法返回一个新的Array Iterator对象,该对象包含数组中每个索引的键/值对。

a.entries()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/entries

例子

var array1 = ['a', 'b', 'c'];

var iterator1 = array1.entries();

console.log(iterator1.next().value);
// expected output: Array [0, "a"]

console.log(iterator1.next().value);
// expected output: Array [1, "b"]

.every

无突变

描述

every() 方法测试数组的所有元素是否都通过了指定函数的测试。

Array.prototype.every ( callbackfn [ , thisArg ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/every

例子

function isBelowThreshold(currentValue) {
  return currentValue < 40;
}

var array1 = [1, 30, 39, 29, 10, 13];

console.log(array1.every(isBelowThreshold));
// expected output: true

.fill()

变异

描述

fill() 方法用一个固定值填充一个数组中从起始索引到终止索引内的全部元素。不包括终止索引。会修改原数组

arr.fill(value)
arr.fill(value, start)
arr.fill(value, start, end)

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/fill

例子

var array1 = [1, 2, 3, 4];

// fill with 0 from position 2 until position 4
console.log(array1.fill(0, 2, 4));
// expected output: [1, 2, 0, 0]

// fill with 5 from position 1
console.log(array1.fill(5, 1));
// expected output: [1, 5, 5, 5]

console.log(array1.fill(6));
// expected output: [6, 6, 6, 6]

.filter

无突变

描述

filter() 方法创建一个新数组, 其包含通过所提供函数实现的测试的所有元素。 

Array.prototype.filter ( callbackfn [ , thisArg ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/filter

例子

var words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];

const result = words.filter(word => word.length > 6);

console.log(result);
// expected output: Array ["exuberant", "destruction", "present"]

.find()

无突变

描述

find() 方法返回数组中满足提供的测试函数的第一个元素的值。否则返回 undefined。

arr.find(callback[, thisArg])

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/find

例子

var array1 = [5, 12, 8, 130, 44];

var found = array1.find(function(element) {
  return element > 10;
});

console.log(found);
// expected output: 12

.findIndex()

无突变

描述

 findIndex() 方法返回数组中满足提供的测试函数的第一个元素的索引。否则返回-1。

arr.findIndex(callback[, thisArg])

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex

例子

var array1 = [5, 12, 8, 130, 44];

function isLargeNumber(element) {
  return element > 13;
}

console.log(array1.findIndex(isLargeNumber));
// expected output: 3

.forEach

无突变

描述

forEach() 方法对数组的每个元素执行一次提供的函数。

Array.prototype.forEach ( callbackfn [ , thisArg ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

例子

var array1 = ['a', 'b', 'c'];

array1.forEach(function(element) {
  console.log(element);
});

// expected output: "a"
// expected output: "b"
// expected output: "c"

.includes()

无突变

描述

includes() 方法用来判断一个数组是否包含一个指定的值,根据情况,如果包含则返回 true,否则返回false。

arr.includes(searchElement)
arr.includes(searchElement, fromIndex)

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/includes

例子

var array1 = [1, 2, 3];

console.log(array1.includes(2));
// expected output: true

var pets = ['cat', 'dog', 'bat'];

console.log(pets.includes('cat'));
// expected output: true

console.log(pets.includes('at'));
// expected output: false

.indexOf

无突变

描述

indexOf() 方法返回在数组中可以找到一个给定元素的第一个索引,如果不存在,则返回-1。

Array.prototype.indexOf ( searchElement [ , fromIndex ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf

例子

var beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];

console.log(beasts.indexOf('bison'));
// expected output: 1

// start from index 2
console.log(beasts.indexOf('bison', 2));
// expected output: 4

console.log(beasts.indexOf('giraffe'));
// expected output: -1

.join

无突变

描述

join() 方法将一个数组(或一个类数组对象)的所有元素连接成一个字符串并返回这个字符串。如果数组只有一个项目,那么将返回该项目而不使用分隔符。

Array.prototype.join (separator)

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/join

例子

var elements = ['Fire', 'Wind', 'Rain'];

console.log(elements.join());
// expected output: "Fire,Wind,Rain"

console.log(elements.join(''));
// expected output: "FireWindRain"

console.log(elements.join('-'));
// expected output: "Fire-Wind-Rain"

.keys()

无突变

描述

 keys() 方法返回一个包含数组中每个索引键的Array Iterator对象。

arr.keys()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/keys

例子

var array1 = ['a', 'b', 'c'];
var iterator = array1.keys(); 
  
for (let key of iterator) {
  console.log(key); // expected output: 0 1 2
}

.lastIndexOf

无突变

描述

lastIndexOf() 方法返回指定元素(也即有效的 JavaScript 值或变量)在数组中的最后一个的索引,如果不存在则返回 -1。从数组的后面向前查找,从 fromIndex 处开始。

Array.prototype.lastIndexOf ( searchElement [ , fromIndex ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/lastIndexOf

例子

var animals = ['Dodo', 'Tiger', 'Penguin', 'Dodo'];

console.log(animals.lastIndexOf('Dodo'));
// expected output: 3

console.log(animals.lastIndexOf('Tiger'));
// expected output: 1

.map

无突变

描述

map() 方法创建一个新数组,其结果是该数组中的每个元素都调用一个提供的函数后返回的结果。

Array.prototype.map ( callbackfn [ , thisArg ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/map

例子

var array1 = [1, 4, 9, 16];

// pass a function to map
const map1 = array1.map(x => x * 2);

console.log(map1);
// expected output: Array [2, 8, 18, 32]

.pop

变异

描述

pop() 方法从数组中删除最后一个元素,并返回该元素的值。此方法更改数组的长度

Array.prototype.pop ( )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/pop

例子

var plants = ['broccoli', 'cauliflower', 'cabbage', 'kale', 'tomato'];

console.log(plants.pop());
// expected output: "tomato"

console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage", "kale"]

plants.pop();

console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage"]

.push

变异

描述

push() 方法将一个或多个元素添加到数组的末尾,并返回该数组的新长度

Array.prototype.push ( [ item1 [ , item2 [ , … ] ] ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/push

例子

var animals = ['pigs', 'goats', 'sheep'];

console.log(animals.push('cows'));
// expected output: 4

console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows"]

animals.push('chickens');

console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows", "chickens"]

.reduce

无突变

描述

reduce() 方法对数组中的每个元素执行一个由您提供的reducer函数(升序执行),将其结果汇总为单个返回值。

Array.prototype.reduce ( callbackfn [ , initialValue ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

例子

const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10

// 5 + 1 + 2 + 3 + 4
console.log(array1.reduce(reducer, 5));
// expected output: 15

.reduceRight

无突变

描述

reduceRight() 方法接受一个函数作为累加器(accumulator)和数组的每个值(从右到左)将其减少为单个值。

Array.prototype.reduceRight ( callbackfn [ , initialValue ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/ReduceRight

例子

const array1 = [[0, 1], [2, 3], [4, 5]].reduceRight(
  (accumulator, currentValue) => accumulator.concat(currentValue)
);

console.log(array1);
// expected output: Array [4, 5, 2, 3, 0, 1]

.reverse

变异

描述

reverse() 方法将数组中元素的位置颠倒,并返回该数组。该方法会改变原数组

Array.prototype.reverse ( )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/reverse

例子

var array1 = ['one', 'two', 'three'];
console.log('array1: ', array1);
// expected output: Array ['one', 'two', 'three']

var reversed = array1.reverse(); 
console.log('reversed: ', reversed);
// expected output: Array ['three', 'two', 'one']

/* Careful: reverse is destructive. It also changes
the original array */ 
console.log('array1: ', array1);
// expected output: Array ['three', 'two', 'one']

.shift

变异

描述

shift()方法从数组中删除第一个元素,并返回该元素的值。此方法更改数组的长度

Array.prototype.shift ( )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/shift

例子

var array1 = [1, 2, 3];

var firstElement = array1.shift();

console.log(array1);
// expected output: Array [2, 3]

console.log(firstElement);
// expected output: 1

.slice

无突变

描述

slice() 方法返回一个新的数组对象,这一对象是一个由 begin和 end(不包括end)决定的原数组的浅拷贝。原始数组不会被改变

Array.prototype.slice (start, end)

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/slice

例子

var animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];

console.log(animals.slice(2));
// expected output: Array ["camel", "duck", "elephant"]

console.log(animals.slice(2, 4));
// expected output: Array ["camel", "duck"]

console.log(animals.slice(1, 5));
// expected output: Array ["bison", "camel", "duck", "elephant"]

.some

无突变

描述

some() 方法测试是否至少有一个元素通过由提供的函数实现的测试。

Array.prototype.some ( callbackfn [ , thisArg ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/some

例子

var array = [1, 2, 3, 4, 5];

var even = function(element) {
  // checks whether an element is even
  return element % 2 === 0;
};

console.log(array.some(even));
// expected output: true

.sort

无突变

描述

sort() 方法用原地算法对数组的元素进行排序,并返回数组。排序算法现在是稳定的。默认排序顺序是根据字符串Unicode码点。

Array.prototype.sort (comparefn)

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

例子

var numbers = [4, 2, 5, 1, 3];
numbers.sort(function(a, b) {
  return a - b;
});
console.log(numbers);

也可以写成:
var numbers = [4, 2, 5, 1, 3]; 
numbers.sort((a, b) => a - b); 
console.log(numbers);

.splice

变异

描述

splice() 方法通过删除或替换现有元素或者原地添加新的元素来修改数组,并以数组形式返回被修改的内容。此方法会改变原数组。

Array.prototype.splice (start, deleteCount [ , item1 [ , item2 [ , … ] ] ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/splice

例子

var months = ['Jan', 'March', 'April', 'June'];
months.splice(1, 0, 'Feb');
// inserts at 1st index position
console.log(months);
// expected output: Array ['Jan', 'Feb', 'March', 'April', 'June']

months.splice(4, 1, 'May');
// replaces 1 element at 4th index
console.log(months);
// expected output: Array ['Jan', 'Feb', 'March', 'April', 'May']

.toLocaleString

无突变

描述

 toLocaleString() 返回一个字符串表示数组中的元素。数组中的元素将使用各自的 toLocaleString 方法转成字符串,这些字符串将使用一个特定语言环境的字符串(例如一个逗号 ",")隔开。

Array.prototype.toLocaleString ( )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/toLocaleString

例子

var array1 = [1, 'a', new Date('21 Dec 1997 14:12:00 UTC')];
var localeString = array1.toLocaleString('en', {timeZone: "UTC"});

console.log(localeString);
// expected output: "1,a,12/21/1997, 2:12:00 PM",
// This assumes "en" locale and UTC timezone - your results may vary

.toSource()

无突变

描述

toSource() 返回一个字符串,代表该数组的源代码.

arr.toSource()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/toSource

 

.toString

无突变

描述

toString() 返回一个字符串,表示指定的数组及其元素。

Array.prototype.toString ( )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/toString

例子

var array1 = [1, 2, 'a', '1a'];

console.log(array1.toString());
// expected output: "1,2,a,1a"

.unshift

变异

描述

 unshift() 方法将一个或多个元素添加到数组的开头,并返回该数组的新长度。

Array.prototype.unshift ( [ item1 [ , item2 [ , … ] ] ] )

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/unshift

例子

var array1 = [1, 2, 3];

console.log(array1.unshift(4, 5));
// expected output: 5

console.log(array1);
// expected output: Array [4, 5, 1, 2, 3]

.values()

无突变

描述

values() 方法返回一个新的 Array Iterator 对象,该对象包含数组每个索引的值

arr.values()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/values

例子

const array1 = ['a', 'b', 'c'];
const iterator = array1.values();

for (const value of iterator) {
  console.log(value); // expected output: "a" "b" "c"
}

​.flat()

无突变

描述

​flat()方法会按照一个可指定的深度递归遍历数组,并将所有元素与遍历到的子数组中的元素合并为一个新数组返回。Array​.prototype​.flat()最初命名是Array​.prototype​.flatten()。

Array.prototype.flat(depth)

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/flat

例子

var arr1 = [1, 2, [3, 4]];
arr1.flat(); 
// [1, 2, 3, 4]

var arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat();
// [1, 2, 3, 4, [5, 6]]

var arr3 = [1, 2, [3, 4, [5, 6]]];
arr3.flat(2);
// [1, 2, 3, 4, 5, 6]

//使用 Infinity 作为深度,展开任意深度的嵌套数组
arr3.flat(Infinity); 
// [1, 2, 3, 4, 5, 6]

 

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