js常用方法学习

浏览数：27 / 时间：2015年06月09日

array manipulation! The basics.

arr.forEach(callback[, thisArg]) [Array.prototype.forEach()]

说明：为数组中的每个元素执行指定操作

注意：　　

1. There is no way to stop or break a forEach() loop.
2. it always returns the value undefined.

function logArrayElem(elem, index, arr) {
    console.log(‘arr[‘ + index + ‘]:::‘ + elem);
}

[2, 5, 9].forEach(logArrayElem);

/* output:
arr[0]:::2 
arr[1]:::5 
arr[2]:::9 
  */

the use of the ‘thisArg‘ argument。该参数指定后可对其引用 this 关键字

var obj = {
    showResult: function(value, index) {
        var squared = this.calcSquare(value);
        console.log(‘numbers[‘ + index + ‘] = ‘ + value);
    },
    calcSquare: function(x) {
        return x * x;
    }
}
var numbers = [2, 5, 9, 89, 12];
numbers.forEach(function(value, index) { this.showResult(value, index) }, obj);

/* output:
numbers[0] = 2 
numbers[1] = 5 
numbers[2] = 9 
numbers[3] = 89 
numbers[4] = 12 
   */

arr.slice([begin[, end]]) [Array.prototype.slice()]

说明：returns a shallow copy of a portion of an array into a new array object

var myHonda = { color: ‘red‘, wheels: 4, engine: { cylinders: 4, size: 2.2 } };
var myCar = [myHonda, 2, ‘cherry condition‘, ‘purchased 1997‘];
var newCar = myCar.slice(0, 2);
console.log(‘myCar = ‘ + myCar);
console.log(‘newCar = ‘ + newCar);
console.log(‘myCar[0].color = ‘ + myCar[0].engine.size);
console.log(‘newCar[0].color = ‘ + newCar[0].engine.size);

/* output:
myCar = [object Object],2,cherry condition,purchased 1997 
newCar = [object Object],2 
myCar[0].color = red 
newCar[0].color = 2.2 
  */

slice method can also be called to convert Array-like objects / collections to a new Array.

function list() {
    return Array.prototype.slice.call(arguments, 1, 3);
}
var list1 = list(1,2,3,4,5,6);
console.log(‘list1 ==> ‘ + list1);

/* output:
list1 ==> 2,3 
  */

arr.splice([start, deletecount[, item[, item[, ...]]]]) [Array.prototype.splice()]

说明：changes the content of an array by removing existing elements and/or adding new elements.

var myFish = [‘angel‘, ‘clown‘, ‘mandarin‘, ‘surgeon‘];

// removes 0 elements from index 2, and inserts ‘drum‘
var removed = myFish.splice(2, 0, ‘drum‘);
// myFish is [‘angel‘, ‘clown‘, ‘drum‘, ‘mandarin‘, ‘surgeon‘]
// removed is [], no elements removed

// removes 1 element from index 3
removed = myFish.splice(3, 1);
// myFish is [‘angel‘, ‘clown‘, ‘drum‘, ‘surgeon‘]
// removed is [‘mandarin‘]

// removes 1 element from index 2, and inserts ‘trumpet‘
removed = myFish.splice(2, 1, ‘trumpet‘);
// myFish is [‘angel‘, ‘clown‘, ‘trumpet‘, ‘surgeon‘]
// removed is [‘drum‘]

// removes 2 elements from index 0, and inserts ‘parrot‘, ‘anemone‘ and ‘blue‘
removed = myFish.splice(0, 2, ‘parrot‘, ‘anemone‘, ‘blue‘);
// myFish is [‘parrot‘, ‘anemone‘, ‘blue‘, ‘trumpet‘, ‘surgeon‘]
// removed is [‘angel‘, ‘clown‘]

// removes 2 elements from index 3
removed = myFish.splice(3, Number.MAX_VALUE);
// myFish is [‘parrot‘, ‘anemone‘, ‘blue‘]
// removed is [‘trumpet‘, ‘surgeon‘]

push() / pop() — add/remove elements from the end of the array
unshift() / shift() — add/remove elements from the beginning of the array

arr.join([separator = ‘,‘]) [Array.prototype.join()]

说明：joins all elements of an array into a string.

var a = [‘Wind‘, ‘Rain‘, ‘Fire‘];
var myVar1 = a.join();
var myVar2 = a.join(separator = ‘, ‘);
var myVar3 = a.join(separator = ‘ + ‘);
var myVar4 = a.join(‘‘);
console.log(‘myVar1 ==> ‘ + myVar1);
console.log(‘myVar2 ==> ‘ + myVar2);
console.log(‘myVar3 ==> ‘ + myVar3);
console.log(‘myVar4 ==> ‘ + myVar4);

/*
myVar1 ==> Wind,Rain,Fire 
myVar2 ==> Wind, Rain, Fire 
myVar3 ==> Wind + Rain + Fire 
myVar4 ==> WindRainFire 
  */

var new_array = arr.concat(value1[, value2[,...]]) [Array.prototype.concat()]

说明：Arrays and/or values to concatenate into a new array

var alpha = [‘a‘, ‘b‘, ‘c‘],
    numeric = [1, 2, 3];
var alphaNumeric = alpha.concat(numeric);
console.log(‘alphaNumeric ==> ‘ + alphaNumeric);  
var alphaNumeric = alpha.concat(2, 3, [‘你‘, ‘好‘]);
console.log(‘alphaNumeric ==> ‘ + alphaNumeric);  

/* output:
alphaNumeric ==> a,b,c,1,2,3 
alphaNumeric ==> a,b,c,2,3,你,好 
 */

var num1 = [1, 2, 3],
    num2 = [4, 5, 6],
    num3 = [7, 8, 9];

var nums = num1.concat(num2, num3);

console.log(nums); // Result: [1, 2, 3, 4, 5, 6, 7, 8, 9]

concatenates three arrays ↑

arr.unshift([elem1[, ...[, elemN]]])

说明：add the elements to the front of the array.

var arr = [1, 2];

arr.unshift(0); // result of call is 3, the new array length
// arr is [0, 1, 2]

arr.unshift(-2, -1); // = 5
// arr is [-2, -1, 0, 1, 2]

arr.unshift([-3]);
// arr is [[-3], -2, -1, 0, 1, 2]

arr.shift()

removes the first element from an array and returns that element

arr.push(elem1, elem2, elem3)

The elements to add to the end of the array.

var sports = [‘soccer‘, ‘baseball‘];
var total = sports.push(‘football‘, ‘swimming‘);

console.log(sports); // [‘soccer‘, ‘baseball‘, ‘football‘, ‘swimming‘]
console.log(total);  // 4

var vegetables = [‘parsnip‘, ‘potato‘];
var moreVegs = [‘celery‘, ‘beetroot‘];

// Equivalent to vegetables.push(‘celery‘, ‘beetroot‘);
Array.prototype.push.apply(vegetables, moreVegs);

console.log(vegetables); // [‘parsnip‘, ‘potato‘, ‘celery‘, ‘beetroot‘]

 Merge the second array into the first one ↑

arr.pop()

说明：removes the last element from an array and returns that value to the caller

var myFish = [‘angel‘, ‘clown‘, ‘mandarin‘, ‘sturgeon‘];
console.log(myFish); // [‘angel‘, ‘clown‘, ‘mandarin‘, ‘sturgeon‘]

var popped = myFish.pop();
console.log(myFish); // [‘angel‘, ‘clown‘, ‘mandarin‘ ] 
console.log(popped); // ‘sturgeon‘

郑重声明：本站内容如果来自互联网及其他传播媒体，其版权均属原媒体及文章作者所有。转载目的在于传递更多信息及用于网络分享，并不代表本站赞同其观点和对其真实性负责，也不构成任何其他建议。

js常用方法学习