I am currently writing a JS rules engine which at one point needs to evaluate boolean expressions using the eval() function.
Firstly I construct an equation as such:
var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator +
" " + "relation.value";
relation.relatedTrigger.previousValue is the value I want to compare.
relation.operator is the operator (either "==", "!=", <=, "<", "", =").
relation.value is the value I want to compare with.
I then simply pass this string to the eval function and it returns true or false as such:
return eval(equation);
This works absolutely fine (with words and numbers) or all of the operators except for = and <=. E.g. When evaluating the equation:
relation.relatedTrigger.previousValue <= 100
It returns true when previousValue = 0,1,10,100 & all negative numbers but false for everything in between.
I would greatly appreciate the help of anyone to either answer my question or to help me find an alternative solution.
Regards,
Augier.
P.S. I don't need a speech on the insecurities of the eval() function. Any value given to relation.relatedTrigger.previousValue is predefined.
edit: Here is the full function:
function evaluateRelation(relation)
{
console.log("Evaluating relation")
var currentValue;
//if multiple values
if(relation.value.indexOf(";") != -1)
{
var values = relation.value.split(";");
for (x in values)
{
var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator +
" " + "values[x]";
currentValue = eval(equation);
if (currentValue)
return true;
}
return false;
}
//if single value
else
{
//Evaluate the relation and get boolean
var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator +
" " + "relation.value";
console.log("relation.relatedTrigger.previousValue " + relation.relatedTrigger.previousValue);
console.log(equation);
return eval(equation);
}
}
Answer: Provided by KennyTM below. A string comparison doesn't work. Converting to a numerical was needed.
