Using string value as a calculation in JS

Question

I am storing a value in a DB (called generalparameter).

This value is a calculation which I call in the JS code.

The issue is the value is a string but I want it to be a calculation value.

e.g. My DB value is:-

(((this.amount / new_rate) - this.stock_payment).toFixed(2) / (this.amount / new_rate) * 100).toFixed(2)

My code is:-

application.getGeneralParameter('UI','CAL_NEW_MARGIN');

But this yields:-

"(((this.amount / new_rate) - this.stock_payment).toFixed(2) / (this.amount / new_rate) * 100).toFixed(2)"

How do I get rid of the ""?

Thanks.

Ian.

What database and what server language? You should be able to remove the quotes on the server. — mplungjan
– mplungjan, Commented Jul 10, 2015 at 8:34
Like other comments and answers said, eval() is your solution, but be carefull with eval() function, it's unsafe. And it is not good practice to store code like this in database, it's better if you store in db a flag or a identifier that calls the string in the code. It's only a recommendation. Good luck — Marcos Pérez Gude
– Marcos Pérez Gude, Commented Jul 10, 2015 at 8:37

mplungjan · Accepted Answer · 2015-07-10 08:59:02Z

2

This works without the actual eval keyword - Function will however also evaluate so caution is advised if arbitrary strings can be saved in the DB since it will execute in the scope of the website your are on.

var fnString = "(((this.amount / new_rate) - this.stock_payment).toFixed(2) / (this.amount / new_rate) * 100).toFixed(2)",
obj = {
  amount:3.9,
  stock_payment:42,
  calc : Function("var new_rate=6.9; return "+fnString)
}
alert(obj.calc())

edited Jul 10, 2015 at 8:59

answered Jul 10, 2015 at 8:41

mplungjan

180k29 gold badges183 silver badges246 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Bergi Over a year ago

Not sure whether new Function is much better than eval :-) It only works if new_rate is a global variable, for example.

mplungjan Over a year ago

@Bergi - moved new_rate to the function and added an advisory caution.

Erik Inkapööl · Accepted Answer · 2015-07-10 08:32:01Z

0

Try using the eval() function, like so:

eval("(((this.amount / new_rate) - this.stock_payment).toFixed(2) / (this.amount / new_rate) * 100).toFixed(2)");

or like so:

eval(application.getGeneralParameter('UI','CAL_NEW_MARGIN'));

answered Jul 10, 2015 at 8:32

Erik Inkapööl

3882 silver badges11 bronze badges

1 Comment

Ian Thompson Over a year ago

Thanks for the suggestions. eval works, but might not be suitable due to injection issues etc, so I will proceed with care.

Collectives™ on Stack Overflow

Using string value as a calculation in JS

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related