Is using javascript eval() safe for simple calculations in inputs? - Stack Overflow

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I would like to allow user to perform simple calculations in the text inputs, so that typing 2*5 will result in 10. I'm replacing everything but digits with an empty string and then make calculation using eval(). This seems easier and probably faster then parsing it manually.

It's often being said that eval() is unsafe, so I would like to hear is there any danger or drawback of using it in this situation.

function (input) {
  value = input.value.replace(/[^-\d/*+.]/g, '');
  input.value=eval(value);
}

I would like to allow user to perform simple calculations in the text inputs, so that typing 2*5 will result in 10. I'm replacing everything but digits with an empty string and then make calculation using eval(). This seems easier and probably faster then parsing it manually.

It's often being said that eval() is unsafe, so I would like to hear is there any danger or drawback of using it in this situation.

function (input) {
  value = input.value.replace(/[^-\d/*+.]/g, '');
  input.value=eval(value);
}

• javascript
• eval

Share Improve this question Follow asked Dec 24, 2012 at 11:29 Oskar SkuteliOskar Skuteli 65877 silver badges1616 bronze badges 2

• 6 var value sigh – katspaugh Commented Dec 24, 2012 at 11:34
• 2 And then you'll get people asking why 2+2e-3 results in 1 instead of 2.002. Warn the people about invalid input, don't silently throw it away. And try/catch the evaluation, so you can tell the user if it failed. – user1233508 Commented Dec 24, 2012 at 11:42

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2 Answers 2

Sorted by: Reset to default 13

That is safe, not because you are sanitizing it, but because it's all entered by the user and run in their own browser. If they really wanted to enter malicious code, they could do it anyway by using firebug or web inspector, or even using a bookmarklet. Thankfully, there isn't much you can do maliciously with javascript except lock up your own browser :)

this is safe because you are doing input validation before you put it into eval.

besides you should also add:

()%

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