indexOf() 方法可返回某个指定的字符串值在字符串中首次出现的位置。在JS中用arr.indexOf(a),其作用为,进行判断a是否是数组arr中的属性,如果不是返回-1,如果是就返回该属性的位置(该属性的key)
整个例子
var arr = ["a","b","c","a","d","c","e","d","c","a","c"]; var ary=[]; for(let i=0;i<arr.length;i++){ var d=arr[i] if(ary.indexOf(d)==-1){ ary.push(arr[i]) } } console.log(ary)