find、findIndex、indexOf、lastIndexOf、Include

1.find() 返回数组中第一个满足条件的数据
(1)// var num = [10, 20, 30, 40, 50, 60, 70, 80, 90]; var newNum1 = num.find((item, index) => { return item > 40; }) console.log("newNum1 = " + newNum1);//50
2.findIndex() 返回数组中第一个满足条件的索引(从0开始), 不满足返回-1
(1)// var num = [10, 20, 30, 40, 50, 60, 70, 80, 90]; var newNum2 = num.findIndex((item, index) => { return item > 40; }) console.log("newNum2 = " + newNum2);//4
3.indexOf() 返回数组中第一个满足条件的索引(从0开始), 不满足返回-1
(1)arr.indexOf(searchElement[, fromIndex = 0])
(2)// var num = [10, 20, 30, 40, 50, 60, 70, 80, 90]; var newNum3 = num.indexOf(40); var newNum4 = num.indexOf(40, 10);//从索引10的位置开始向后查找 console.log("newNum3 = " + newNum3);//3 console.log("newNum4 = " + newNum4);//-1
4.lastIndexOf() 返回数组中最后一个满足条件的索引(从0开始), 不满足返回-1
(1)var newNum5 = num.lastIndexOf(40); var newNum6 = num.lastIndexOf(40, 1);//从索引1的位置开始向前查找 console.log("newNum5 = " + newNum5);//3 console.log("newNum6 = " + newNum6);//-1
5.include() 判断数组宏是否包含某值，返回 true 或 false
(1)// var num = [10, 20, 30, 40, 50, 60, 70, 80, 90]; var newNum7 = num.includes(40); var newNum8 = num.includes(40, 5);//从索引5的位置开始向后查找 console.log("newNum7 = " + newNum7);//true console.log("newNum8 = " + newNum8);//false