js數組一些基礎使用方法

• 向數組中添加元素：push

var arr =[];
arr.push("新元素");

• 刪除數組中的指定元素：splice

//刪除數組中指定元素“2”

　　var arr = [1,2,5,8,20,19];
　　var arr1 = arr.splice(arr.indexOf(2),1);
　　console.log(arr); //[1, 5, 8, 20, 19]
　　console.log(arr1); //[2]

• 數組去重

var arr = [1,2,5,8,5,5,20,19,5];
var temp = new Set(arr);
arr = Array.from(temp);
console.log(arr);// [1, 2, 5, 8, 20, 19]         

• 數組清空

var arr = [1,2,3];
//方式1
arr = [];
//方式2
arr.length = 0

• 將數組拼接成字符串

var arr = [1,2,5,8,5,5,20,19,5];
arr = arr.join(",")
console.log(arr); // 1,2,5,8,5,5,20,19,5

•  數組元素過濾

var arr = [1,2,3];
var arr1 = [1,2,3,4,5,6,7,8];
var newArr = arr1.filter(item => {
    //滿足這個條件的元素被保留
    return arr.indexOf(item) == -1;
})
console.log(newArr);//[4,5,6,7,8]

• 數組遍歷

//方式一： 數組名.forEach(function(item,index){})

var arrs=["a","b","c","d","e","f","g"];

arrs.forEach(function(item,index){

　　console.log(item);// a b c d e f g ,數組中的元素

　　console.log(index);//0 1 2 3 4 5 6，數組中元素所對應的索引
})

//方式二： for循環

var arrs=["a","b","c","d","e","f","g"];

for(var i = 0; i < arrs.length; i++){
　　console.log(arrs.length);

}

//方式三：for of循環

var arrs=["a","b","c","d","e","f","g"];

for(var value of arrs){
　　console.log(value);

}