程式碼示例：

//indexOf() 方法可返回某個指定的字串值在字串中首次出現的位置。

//利用indexOf()函式統計陣列arr["a","b","d","d","c","d","d"]中元素d出現的次數,

//並同時返回其對應的所有索引下標

var arr=new Array("a","b","d","d","c","d","d");

var numarr = new Array();

var indexnum=0,num;

for (var i=0;i<arr.length;i++) {

num = arr.indexOf("d",0); //獲得第一個d的下表

if(num!=-1){ //記錄個數

numarr[indexnum]=num;

indexnum++;

}

arr[num]="c";

}

document.write("元素d出現的次數"+indexnum+"<br />");

document.write("所有索引下標:")

for(var i=0;i<numarr.length;i++){

document.write(numarr[i]+",");

}