How to use String representation of object property, operator, and value?

Question

I'm trying to use a string value of say, "[ScheduledDate] < '11/1/2011'", and test for a bool value on an object like "item". But I can't seem to be able to figure out a way to do it successfully. I'm not wanting to use the eval function, but if it's the only way, then I guess I will have to. below is an example of the function I'm trying to use.

function _filterItem2() {
        var item = { ScheduledDate: '1/1/2012' };
        var filterExpression = "[ScheduledDate] < '11/1/2011'";

        var result = item[filterExpression];  // This is where I'm not sure.

        return result;
    }

Do you control the filterExpression or is it supplied by a third party (or user)? — apsillers
– apsillers, Commented Jun 18, 2012 at 18:14

Bergi · Accepted Answer · 2012-06-18 18:23:17Z

2

No, item[filterExpression] would just return the property named like your string.

Instead, you should store your filter expression as an object:

var filter = {
    propname: "ScheduledDate",
    operator: "<",
    value: "1/1/2012"
};

Then get your comparison values:

var val1 = item[filter.propname],
    val2 = filter.value;

and now comes the tricky part. You are right, you should not use eval. But there is no possibility to get the corresponding functions from operator names, so you will need to code them yourself. You might use a switch statement or a map like this:

var operators = {
    "<": function(a,b){return a<b;},
    ">": function(a,b){return a>b;},
    ...
};
var bool = operators[filter.operator](val1, val2);

answered Jun 18, 2012 at 18:23

Bergi

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2 Comments

jhorton Over a year ago

Worked perfectly. I did two mappings, one that would use regex to get what the operator would be from the expression, and the other like the one you have above. Thanks for the help

Bergi Over a year ago

See also here for a more dynamic approach

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