Javascript - Convert HTML input string into mathematical evaluation

Question

I have been wondering if is possible to use a HTML <input id="in"> (which I could enter lets say 25 / 6 * 3) and output the mathematical evaluation with Javascript, I have written up something which very understandably did not work, would there be any way to make it work?

function go() {
    var x = $("#in").val();
    alert(parseInt(x))
}

Your answers are much appreciated

Your question is not very clear. What does #in contain?

Vivin Paliath
– Vivin Paliath

2014-02-10 15:41:48 +00:00
Commented Feb 10, 2014 at 15:41 — Vivin Paliath
– Vivin Paliath, Commented Feb 10, 2014 at 15:41
Please provide me code at fiddle

Jain
– Jain

2014-02-10 15:41:49 +00:00
Commented Feb 10, 2014 at 15:41 — Jain
– Jain, Commented Feb 10, 2014 at 15:41
I'd think eval() would do it. jsfiddle.net/j08691/Vajh4

j08691
– j08691

2014-02-10 15:44:01 +00:00
Commented Feb 10, 2014 at 15:44 — j08691
– j08691, Commented Feb 10, 2014 at 15:44
I'd use eval, but first make sure it isn't dangerous.

MightyPork
– MightyPork

2014-02-10 16:14:06 +00:00
Commented Feb 10, 2014 at 16:14 — MightyPork
– MightyPork, Commented Feb 10, 2014 at 16:14

Ian · Accepted Answer · 2014-02-10 15:43:29Z

2

Yes you can using the eval() function. Assuming you're input is going to take a value then you can simply call eval(myString) which should return the result.

For example if you execute the following:

alert(eval('3 + 4')); // alerts 7

Be wary though in that anything you do really shouldn't be saved as this could lead to javascript attacks if someone is able to submit some javascript that will run on someone elses browser.

answered Feb 10, 2014 at 15:43

Ian

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Comments

Vivin Paliath · Accepted Answer · 2014-02-10 15:45:00Z

0

Yes, it is possible to do what you're asking; you just have to use eval(). However, using eval() is not very safe. since this means that any JavasScript code inside #in will be evaluated, which is probably not what you want.

A better way to do this would be to write a parser to parse the mathematical expression and build a syntax tree and then evaluate that.

answered Feb 10, 2014 at 15:45

Vivin Paliath

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2 Comments

j08691 Over a year ago

Well considering the person typing in the page would only be affecting their own browser, I don't see why any malicious results would be anyone's fault but their own.

Vivin Paliath Over a year ago

@j08691 Of course; I wasn't implying maliciousness in this situation but merely alerting the OP to the caveats involved with the use of eval().

Jos de Jong · Accepted Answer · 2014-12-22 12:29:23Z

0

You can use the expression parser of math.js

alert(math.eval('3 + 4'));

edited Dec 22, 2014 at 12:29

answered Feb 11, 2014 at 19:58

Jos de Jong

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