Increase/decrease textfield value with javascript

I'm having trouble in doing a javascript that will do the following:

Increase/decrease number inside textbox when image clicked. setting a limit for that textbox (not below zero, not a开发者_StackOverflow中文版bove x)

please know i have many text boxes in the same page, so how can this issue be fixed?

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You don't need to (and shouldn't) set ids for each and every image and input field. You will need to set name attributes for each input field though (so your server code can tell them apart - but not for JS).

If the "add" section for each row looks like:

<div>
  <img src='minus.png' onclick="increment(this.parentNode.getElementsByTagName('input')[0]);" />
  <input type='text' name='product_1010101011' />
  <img src='plus.png' onclick="decrement(this.parentNode.getElementsByTagName('input')[0]);" />
</div>

use this javascript:

function increment(myInput) {
  // use Mike Samuel's code here
  myInput.value = (+myInput.value + 1) || 0;
}
function decrement(myInput) {
  // use Mike Samuel's code here
  myInput.value = (myInput.value - 1) || 0;
}

---

I think this should get you going:

<form>
    <input type="button" id="minus" value="-" 
    onClick="textb.value = (textb.value-1)">
    <input type="text" id="textb" name="name" value="1" />
    <input type="button" value="+" 
    onClick="textb.value = (+textb.value+1)">
</form>

Live example here

---

To increment

myInput.value = (+myInput.value + 1) || 0;

To decrement

myInput.value = (myInput.value - 1) || 0;

The || 0 will reset any value that doesn't parse as an integer to a default value, 0.