js判断数组，对象是否存在某一未知元素

1 var obj = {
2     aa:‘1111‘,
3     bb:‘2222‘,
4     cc: ‘3333‘
5 };
6 var str=‘aa‘;
7 if(str in obj){
8     console.log(obj[str]);
9 }

1 var obj = {
2     aa:‘1111‘,
3     bb:‘2222‘,
4     cc: ‘3333‘
5 };
6 var str=‘toString‘;
7 if(str in obj){
8     console.log(obj[str]);
9 }

 1 var obj = {
 2     aa: ‘1111‘,
 3     bb: ‘2222‘,
 4     cc: ‘3333‘
 5 };
 6 var str = ‘aa‘;
 7 if (obj.hasOwnProperty(str)) {
 8     console.log(111);
 9 }else{
10     console.log(222);
11 }

1 var test = [‘a‘, 3455, -1];
2 
3 function isInArray(arr, val) {
4     var testStr = arr.join(‘,‘);
5     return testStr.indexOf(val) != -1
6 };
7 alert(isInArray(test, ‘a‘));

Array.prototype.contains = function(obj) {
    var len = this.length;
    while (len--) {
        if (this[len] === obj) {
            return true
        }
    }
    return false;
};

Array.prototype.contains = function(obj) {
    var len = this.length;
    for (var i = 0; i < len; i++) {
        if (this[i] === obj) {
            return true
        }
    }
    return false;
}