If the input you want to change is bound to something, you don’t want to update the text input value directly in the DOM. Instead, you should update the data property associated to that field (the model prop).
But I guess the problem with your code is jQuery.val() usage. Change your increase function to something similar to the following:
Note that when you read the value of something you call the .val() function with no parameters (e.g. $('.selector').val()) When you want to write the value into something, you pass the value as the parameter of that function (e.g. $('.selector').val(1)).
thank you I changed the code a bit so i can see the value and have it like this now:
i understand the .val part of your answer thanks
var inputField = $("#qnty-bulk");
var inputValue = inputField.val();
//inputValue = (inputValue != null && inputValue != '' ? (isNaN(inputValue) ? 0 : inputValue) : 0);
inputValue++;
console.log(inputField.val()); // i see this value go up each time on the click
inputField.val(inputField.val()); //but no value shows in {{ qnty }}