javascript: can i avoid eval in this example?

Question

I have to deal with a customers Javascript Framework for a very specific task.

I have this html:

<div data-foo="(#a = #b)">...loading</div>

In Javascript I get the data-*-Attribute as a string:

foo = '(#a = #b)'

then an ajax call is made with the following answer:

#a=1, #b=1

next the tags are replaced with the values from ajax call (and the operator is replaced as well):

foo = '(1 == 1)'

then foo is evaluated with eval();

result = eval(foo)  // true

Is there a way to avoid eval()? I always have to evaluate string like '(0 == 1)' or '((0 == 0) && (1 == 0))'. I have no chance to influence servers resonse. I need a good and safe way to evaluate the strings to true or false.

EDIT:

possible strings are:

'(0 == 0)'
'(0 == 1)'
'(0 > 5)'
'(117 > 0)'
'((0 == 1) && (11 == 11))'
'((0 == 1) || (0 == 0))'
'(((0 < 1) || (0 == 0) ) && (33 != 11))'
...and so on!

the result always need to be true or false.

Yes, that's possible, but 1) what are the possible strings ? 2) why do you want to avoid eval ? — Denys Séguret, May 29 '13 at 18:43
The real question is why `eval` was used in the first place. This program flow smells something awful. — zzzzBov, May 29 '13 at 20:45

score 2 · Accepted Answer · answered May 29 '13 at 19:07

2

Here are some resources that might solve your problem:

There are many more out there. Search "javascript expression parser".

answered May 29 '13 at 19:07

Trevor Dixon

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those expression parsers are to heavy for my application. Can someone suggest a lightweight expression parser for the strings I posted above? – user2433625 May 30 '13 at 17:08

javascript: can i avoid eval in this example?

1 Answers1