jQuery/Javascript Invalid left-hand side in assignment

Question

I am using this relatively simple code:

var height = help ? 'minus' : 'plus';
var prop = $('#properties');

if(height == 'minus'){
    prop.height(prop.height() -= 206);
} else {
    prop.height(prop.height() += 206);
}

It fails on both lines that do the adding/subtracting! Any ideas?

Answer 1

The -= operator equals operand = operand - value which in your case would look like

prop.height() = prop.height() - 206;

which obviously will fail. You just need the minus operator to accomplish that task.

prop.height(prop.height() - 206);

will do it.

Answer 2

you can't -= a method.

either you need to prop.height(prop.height() - 206); or collect the value first and then -= it like...

var h = prop.height();
h -= 206
 prop.height( h);