string.indexof(x)返回查询的位置
'zhangyachao'.includes('a',0)//true
'zhangyachao'.includes('a',11)//false
'zhangyachao'.indexOf('yachao')//5
'zhangyachao'.indexOf('a')//2
2,forEach(数组的循环不能中断)
array.forEach(function(currentValue,index,array){})
//必须 currentValue:当前的元素
//可选参数 index:当前元素的索引值
//可选参数 array :当前元素所属的数组对象
例子: [2,3,4,5,6,7,8,9].forEach((value,index,arr)=>{console.log(value,index,arr)})
//2 0 [2, 3, 4, 5, 6, 7, 8, 9]
// 1 [2, 3, 4, 5, 6, 7, 8, 9]
// 4 2 [2, 3, 4, 5, 6, 7, 8, 9]
// 5 3 [2, 3, 4, 5, 6, 7, 8, 9]
// 6 4 [2, 3, 4, 5, 6, 7, 8, 9]
//7 5 [2, 3, 4, 5, 6, 7, 8, 9]
// 8 6 [2, 3, 4, 5, 6, 7, 8, 9]
// 9 7 [2, 3, 4, 5, 6, 7, 8, 9]