Increment variable by more than 1?

Question

Here's my script :

function itemQuantityHandler(operation, cart_item) {
  var v = cart_item.quantity;

  //add one
  if (operation === 'add' && v < settings.productBuyLimit) {
    v++;
  }

  //substract one
  if (operation === 'subtract' && v > 1) {
    v--;
  }

  //update quantity in shopping cart
  $('.item-quantity').text(v);

  //save new quantity to cart
  cart_item.quantity = v;
}

What I need is to increase v (cart_item.quantity) by more than one. Here, it's using v++, but it's only increasing by 1. How can I change this to make it increase by 4 every time I click on the plus icon?

I tried

v++ +4

But it's not working.

If you don't know how to add 4 to a number, I'd really suggest running through a basic programming tutorial. — cliffs of insanity, May 17 '12 at 20:04

helpermethod · Accepted Answer · 2012-05-17T20:13:58.827

43

Use a compound assignment operator:

v += 4;

edited May 17 '12 at 20:13

answered May 17 '12 at 20:03

helpermethod

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1

Not equivalent: `v += 4` only evaluates the expression once, which is good when it's a long expression or it has side effects. – We Are All Monica May 17 '12 at 20:06
v+=1 acts like ++v not v++ – Ali Apr 15 '21 at 11:27

We Are All Monica · Answer 2 · 2017-02-27T07:38:08.387

22

Use variable += value; to increment by more than one:

v += 4;

It works with some other operators too:

v -= 4;
v *= 4;
v /= 4;
v %= 4;
v <<= 1;
v >>= 4;

edited Feb 27 '17 at 07:38

answered May 17 '12 at 20:02

We Are All Monica

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For reference: See [Addition Assignment](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Assignment_Operators#Addition_assignment) (`+=`) and [Subtraction Assignment](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Assignment_Operators#Subtraction_assignment) (`-=`) operators. – showdev Aug 05 '15 at 20:52
||= and &&= don't seem to exist in JavaScript. |= and &= perform bitwise assignment operators which are just as good if you're not doing direct === comparisons to actual booleans. – Edwin Feb 04 '17 at 00:16
You're right @Csit - I must have been thinking in a different language when I wrote this. – We Are All Monica Feb 27 '17 at 07:38

score 3 · Answer 3 · answered May 17 '12 at 20:02

3

To increase v by n: v += n

answered May 17 '12 at 20:02

Kvam

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score 0 · Answer 4 · answered May 17 '12 at 20:01

Try this:

//event handler for item quantity in shopping cart
    function itemQuantityHandler(p, a) {
        //get current quantity from cart
        var filter = /(\w+)::(\w+)/.exec(p.id);
        var cart_item = cart[filter[1]][filter[2]];
        var v = cart_item.quantity;


        //add four
        if (a.indexOf('add') != -1) {
            if(v < settings.productBuyLimit) v += 4;
        }
        //substract one
        if (a.indexOf('subtract') != -1) {
            if (v > 1) v--;

        }
        //update quantity in shopping cart
        $(p).find('.item-quantity').text(v);
        //save new quantity to cart
        cart_item.quantity = v;
        //update price for item
      $(p).find('.item-price').text((cart_item.price*v).toFixed(settings.numberPrecision));
        //update total counters 
        countCartTotal();
    }

score -1 · Answer 5 · answered Mar 15 '20 at 04:16

-1

var i = 0; function buttonClick() { x = ++i*10 +10; }

answered Mar 15 '20 at 04:16

Flavio

1

Increment variable by more than 1?

5 Answers5

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