字符串方法indexOf

var a="sdafasfaklfahsjkjdhalfkajsflkasjdkajsfhakjsf"
var pos=a.indexOf('a')
var arr=[]

while(pos>-1){
    console.log(a.charAt(pos),pos)
    arr.push(pos)
    pos=a.indexOf('a',pos+1)   
}
console.log(arr)