运行此程序后出现错误，Uncaught TypeError：无法读取未定义的属性“ push”

Question

var nums = [45, 35, 25, 15, 1, 25, 35,];
var dup;
    for(var i = 0; i<nums.length; i++){
    for(var j = nums[i+1]; j<nums.length; j++){
    if(nums[i] == nums[j]) {
    dup.push(nums[i]);
    alert(dup);
    }
    }
}

Please help me in this program, when I am running this program I am getting this error. I am trying to push duplicate value in dup variable. Uncaught TypeError: Cannot read property 'push' of undefined

Answer 1

var nums = [45, 35, 25, 15, 1, 25, 35,];
var dup = []; // Initialize this array

for(var i = 0; i<nums.length; i++) {
  for(var j = i+1; j<nums.length; j++) { // Change this line
    if(nums[i] == nums[j]) {
      dup.push(nums[i]);
      alert(dup);
    }
  }
}