Question

I have ‘n’ numbers in a TEXTAREA on a form. After the user enters some value in the TEXTAREA, I need to validate it’s not a duplicate of any other value.

Example:

TEXTAREA_1 value =
10
20
30
40
10

It should alert and say ‘value 10 was entered more than once’. Please help me with the JavaScript.

Answer 1

var nums = textarea.value.split('\n').sort();
var prev;
for (var i = 0; i < nums.length; i++ ) {
    if (prev && nums[i] == prev) {
        alert('value ' + prev + ' was entered more than once');
        break;
    }
    prev = nums[i];
}