js陣列方法的總結

1、隊尾插入push

var colors = ["red","green"];

colors.push("black"):
console.log(colors); //["red","green","black"]

var colors = ["red","green","black"];

var item = colors.pop();
console.log(item); //"black"

var colors = ["red","green"];

colors.unshift("black");
var item = colors.pop();
console.log(item); //"black"

var colors = ["red","green","black"];

colors.shift();
console.log(colors); //["green","black"]

var colors = ["red","green","black"];

var colors2 = colors.concat("yellow",["blue","brown"]);
console.log(colors); //["red","green","black"]
console.log(colors2); //["red","green","black","yellow","blue","brown"]

只傳乙個引數：從陣列這個引數的下標開始擷取一直到陣列結束。

var colors = ["red","green","black"];

colors.slice(1); //["green","black"]
console.log(colors); //["red","green","black"]

var colors = ["red","green","black","yellow","blue","brown"];

colors.slice(1,3)//從位置1開始，到位置2結束["green","black"];

有三種用法：

var colors = ["red","green","black"];

var removed = colors.splice(0,1);
console.log(colors); //["green","black"]
console.log(removed); //["red"]
removed = colors.splice(1,0,"yellow","orange");
console.log(colors); //["green","yellow","orange","black"]
console.log(removed); //
removed = colors.splice(1,1,"red","purple");
console.log(colors); //["green","red","purple","orange","black"]
console.log(removed); //["yellow"]

indexof()和lastindexof()都接收兩個引數，第乙個引數是要查詢的項，第二個（可選）查詢開始的位置，indexof()是從陣列頭開始查，lastindexof()是從陣列尾開始查詢。

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

console.log(numbers.indexof(4)); //3
console.log(numbers.lastindexof(4)); //5
console.log(numbers.indexof(4,4)); //5
var person = ;
var people = ;
var morepeople = [person];
console.log(people.indexof(person)); //-1
console.log(morepeople.indexof(person)); //0

查詢符合條件的第一項

var inventory = [

,];

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

var everyresult = numbers.every((item, index, array) => );
console.log(everyresult); //false
var someresult = numbers.some((item, index, array) => );
console.log(someresult); //true

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

var filterresult = numbers.filter((item, index, array) => );
console.log(filterresult); //[3,4,5,4,3]

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

var mapresult = numbers.map((item, index, array) => );
console.log(mapresult); //[2,4,6,8,10,8,6,4,2]

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

numbers.foreach((item, index, array) => );

這兩個方法都會迭代陣列的所有項，然後構建乙個最終返回的值。

reduce（）方法從陣列的第一項開始，逐個遍歷到最後。                                  
reduceright（）則從陣列的最後一項開始，向前遍歷到第一項。

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

var sum = values.reduce((prev, cur, index, array) => );
console.log(sum); //15

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

var sum = values.reduceright((prev, cur, index, array) => 
);console.log(sum); //15

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