js实现从数组里随机获取元素

var arry = [1,5,9,7],
    new_arry = [],
    n = 0,
    len = arry.length;
for(;n<len;n++){
    new_arry.push(arry[n]);
}

var arry = [1,5,9,7],
    new_arry = arry.concat();
console.log(new_arry);

var arry = [1,5,9,7],
    new_arry = arry.slice(0);
console.log(new_arry);

function getRandom(opt) {
    var old_arry = opt.arry,
        range = opt.range;
    //防止超过数组的长度
    range = range > old_arry.length?old_arry.length:range;
    var newArray = [].concat(old_arry), //拷贝原数组进行操作就不会破坏原数组
        valArray = [];
    for (var n = 0; n < range; n++) {
        var r = Math.floor(Math.random() (newArray.length));
        valArray.push(newArray[r]);
        //在原数组删掉，然后在下轮循环中就可以避免重复获取
        newArray.splice(r, 1);
    }
    return valArray;
}
var new_val = getRandom({'arry':[1,6,8,0,3],'range':3});
console.log(new_val);